diff --git a/README.md b/README.md
index ba68878..b2028b1 100644
--- a/README.md
+++ b/README.md
@@ -24,11 +24,9 @@ You can download and test the latest nightly build from https://github.com/nakst
 
 These builds are configured to run on emulators only, to make testing easier. Builds for real hardware are coming soon :)
 
-## Source
+## Building
 
-See `help/Building.md` for a description of how to build and test the system from source.
-
-For an overview of the files in the source tree, see `help/Source Map.md`.
+See `help/Building.md` for a description of how to build and test the system.
 
 ## Features
 
diff --git a/apps/file_manager.ini b/apps/file_manager.ini
index ede7957..6f2487d 100644
--- a/apps/file_manager.ini
+++ b/apps/file_manager.ini
@@ -13,108 +13,131 @@ background_service=1
 source=apps/file_manager/main.cpp
 
 [file_type]
-extension=esx
+match=ext:esx
 name=Executable
 icon=icon_application_default_icon
+uuid=BF-88-E4-DD-71-E8-5F-DE-16-C5-AF-33-41-C7-A2-96
 
 [file_type]
-extension=ini
+match=ext:ini
 name=Configuration file
 icon=icon_application_x_desktop
+uuid=81-72-43-29-E5-37-89-51-8E-22-A0-67-A5-B9-42-2C
+textual=1
 
 [file_type]
-extension=esx_symbols
-name=Debugging data
-icon=icon_extension
-
-[file_type]
-extension=exe
-name=PC executable
-icon=icon_application_x_ms_dos_executable
-
-[file_type]
-extension=png
+match=ext:png
 name=PNG image
 icon=icon_image_x_generic
 has_thumbnail_generator=1
+uuid=59-21-05-4D-34-40-AB-61-EC-F9-7D-5C-6E-04-96-AE
 
 [file_type]
-extension=jpg
+match=ext:jpg,ext:jpeg
 name=JPG image
 icon=icon_image_x_generic
 has_thumbnail_generator=1
+uuid=D8-C2-13-B0-53-64-82-11-48-7B-5B-64-0F-92-B9-38
 
 [file_type]
-extension=ttf
+match=ext:tga
+name=TGA image
+icon=icon_image_x_generic
+has_thumbnail_generator=1
+uuid=69-62-4E-28-A1-E1-7B-35-64-2E-36-01-65-91-BE-A1
+
+[file_type]
+match=ext:bmp
+name=BMP image
+icon=icon_image_x_generic
+has_thumbnail_generator=1
+uuid=40-15-B7-82-99-6D-D5-41-96-D5-3B-6D-A6-5F-07-34
+
+[file_type]
+match=ext:ttf
 name=TrueType font
 icon=icon_font_x_generic
+uuid=DA-BF-EC-06-31-8A-67-B6-E3-95-BC-D1-92-D2-9A-56
 
 [file_type]
-extension=otf
+match=ext:otf
 name=OpenType font
 icon=icon_font_x_generic
+uuid=E7-2B-BB-E7-FF-75-32-E0-4E-75-41-C0-D2-ED-80-56
 
 [file_type]
-extension=a
+match=ext:a
 name=Static library
 icon=icon_extension
+uuid=7D-39-BF-18-9E-07-BC-D3-4F-9F-87-EC-6F-70-65-5D
 
 [file_type]
-extension=dat
-name=Database
+match=ext:dat
+name=Application data
 icon=icon_office_database
+uuid=B5-32-22-14-01-CB-D0-1D-A2-55-08-C7-0D-46-86-53
 
 [file_type]
-extension=icon_pack
-name=Icon pack
-icon=icon_package_x_generic
-
-[file_type]
-extension=ekm
+match=ext:ekm
 name=Kernel module
 icon=icon_extension
+uuid=80-6D-8E-D6-C7-45-AD-A7-03-5B-B3-64-C5-0A-EE-C6
 
 [file_type]
-extension=o
+match=ext:o
 name=Binary object
 icon=icon_extension
+uuid=B5-19-F2-0D-AD-4F-D4-C9-A4-BF-97-E4-5E-4C-55-00
 
 [file_type]
-extension=c
+match=ext:c
 name=C source
 icon=icon_text_x_csrc
+uuid=36-02-D3-AC-6C-DE-8D-31-FA-70-B2-DA-FA-81-53-69
+textual=1
 
 [file_type]
-extension=cpp
+match=ext:cpp
 name=C++ source
 icon=icon_text_x_csrc
+uuid=35-84-A6-0E-52-28-BA-AB-CA-74-14-F4-E1-15-CA-5F
+textual=1
 
 [file_type]
-extension=h
+match=ext:h
 name=C header
 icon=icon_text_x_csrc
+uuid=D1-16-C4-C1-7B-C0-ED-4F-CA-AC-18-05-32-1D-56-32
+textual=1
 
 [file_type]
-extension=txt
+match=ext:txt
 name=Text file
 icon=icon_text
+uuid=25-65-4C-89-E7-29-EA-9E-B5-BE-B5-CA-A7-60-BD-3D
+textual=1
 
 [file_type]
-extension=md
+match=ext:md
 name=Markdown file
 icon=icon_text_markdown
+uuid=B1-C3-9E-56-C9-B0-85-D6-AF-98-12-1C-2E-29-8D-24
+textual=1
 
 [file_type]
-extension=ogg
+match=ext:ogg
 name=OGG audio
 icon=icon_audio_x_generic
+uuid=E5-14-14-ED-4D-67-C0-D0-62-A1-A4-D4-F5-82-A7-88
 
 [file_type]
-extension=mp4
+match=ext:mp4
 name=MP4 video
 icon=icon_view_list_video_symbolic
+uuid=02-76-E1-41-B8-54-19-A9-05-8D-C1-3F-6E-8F-D7-9E
 
 [file_type]
-extension=wav
+match=ext:wav
 name=Wave audio
 icon=icon_audio_x_generic
+uuid=87-BC-A1-A1-25-76-26-5C-8F-94-D6-D8-35-B6-7A-9F
diff --git a/apps/file_manager/commands.cpp b/apps/file_manager/commands.cpp
index e407593..b82627f 100644
--- a/apps/file_manager/commands.cpp
+++ b/apps/file_manager/commands.cpp
@@ -22,10 +22,11 @@ void CommandRename(Instance *instance, EsElement *, EsCommand *) {
 	instance->rename.index = index;
 
 	FolderEntry *entry = instance->listContents[index].entry;
+	ptrdiff_t extensionOffset = PathGetExtension(entry->GetName()).text - entry->name;
 
-	if (entry->extensionOffset != entry->nameBytes) {
+	if (extensionOffset != entry->nameBytes) {
 		// Don't include the file extension in the initial selection.
-		EsTextboxSetSelection(instance->rename.textbox, 0, 0, 0, entry->extensionOffset - 1);
+		EsTextboxSetSelection(instance->rename.textbox, 0, 0, 0, extensionOffset - 1);
 	}
 
 	instance->rename.textbox->messageUser = [] (EsElement *element, EsMessage *message) {
@@ -499,23 +500,32 @@ void InstanceRegisterCommands(Instance *instance) {
 	EsCommandRegister(&instance->commandRename, instance, INTERFACE_STRING(FileManagerRenameAction), CommandRename, stableCommandID++, "F2");
 
 	EsCommandRegister(&instance->commandViewDetails, instance, INTERFACE_STRING(CommonListViewTypeDetails), [] (Instance *instance, EsElement *, EsCommand *) {
-		uint8_t old = instance->viewSettings.viewType;
+		if (instance->viewSettings.viewType != VIEW_DETAILS) {
+			EsElementStartTransition(instance->list, ES_TRANSITION_FADE, ES_ELEMENT_TRANSITION_CONTENT_ONLY, 1.0f);
+		}
+
 		instance->viewSettings.viewType = VIEW_DETAILS;
-		InstanceRefreshViewType(instance, old != instance->viewSettings.viewType);
+		InstanceRefreshViewType(instance);
 		InstanceViewSettingsUpdated(instance);
 	}, stableCommandID++);
 
 	EsCommandRegister(&instance->commandViewTiles, instance, INTERFACE_STRING(CommonListViewTypeTiles), [] (Instance *instance, EsElement *, EsCommand *) {
-		uint8_t old = instance->viewSettings.viewType;
+		if (instance->viewSettings.viewType != VIEW_TILES) {
+			EsElementStartTransition(instance->list, ES_TRANSITION_FADE, ES_ELEMENT_TRANSITION_CONTENT_ONLY, 1.0f);
+		}
+
 		instance->viewSettings.viewType = VIEW_TILES;
-		InstanceRefreshViewType(instance, old != instance->viewSettings.viewType);
+		InstanceRefreshViewType(instance);
 		InstanceViewSettingsUpdated(instance);
 	}, stableCommandID++);
 
 	EsCommandRegister(&instance->commandViewThumbnails, instance, INTERFACE_STRING(CommonListViewTypeThumbnails), [] (Instance *instance, EsElement *, EsCommand *) {
-		uint8_t old = instance->viewSettings.viewType;
+		if (instance->viewSettings.viewType != VIEW_THUMBNAILS) {
+			EsElementStartTransition(instance->list, ES_TRANSITION_FADE, ES_ELEMENT_TRANSITION_CONTENT_ONLY, 1.0f);
+		}
+
 		instance->viewSettings.viewType = VIEW_THUMBNAILS;
-		InstanceRefreshViewType(instance, old != instance->viewSettings.viewType);
+		InstanceRefreshViewType(instance);
 		InstanceViewSettingsUpdated(instance);
 	}, stableCommandID++);
 
diff --git a/apps/file_manager/folder.cpp b/apps/file_manager/folder.cpp
index df46230..1590be9 100644
--- a/apps/file_manager/folder.cpp
+++ b/apps/file_manager/folder.cpp
@@ -394,7 +394,6 @@ FolderEntry *FolderAddEntry(Folder *folder, const char *_name, size_t nameBytes,
 		entry->handles = 1; 
 		entry->name = name;
 		entry->nameBytes = nameBytes;
-		entry->extensionOffset = PathGetExtension(entry->GetName()).text - name;
 		entry->internalName = name;
 		entry->internalNameBytes = nameBytes;
 
@@ -417,6 +416,7 @@ FolderEntry *FolderAddEntry(Folder *folder, const char *_name, size_t nameBytes,
 	entry->size = information->fileSize;
 	entry->isFolder = information->type == ES_NODE_DIRECTORY;
 	entry->sizeUnknown = entry->isFolder && information->directoryChildren == ES_DIRECTORY_CHILDREN_UNKNOWN;
+	entry->contentType = information->contentType;
 
 	return entry;
 }
@@ -459,12 +459,26 @@ uint64_t FolderRemoveEntryAndUpdateInstances(Folder *folder, const char *name, s
 	return id;
 }
 
-void FolderFileUpdatedAtPath(String path, Instance *instance) {
+void FolderFileUpdatedAtPath(String path, Instance *instance, bool setGuessedContentType = false) {
 	path = PathRemoveTrailingSlash(path);
 	String file = PathGetName(path);
 	String folder = PathGetParent(path);
 	EsDirectoryChild information = {};
 	bool add = ES_SUCCESS == EsPathQueryInformation(STRING(path), &information);
+	EsUniqueIdentifier zeroIdentifier = {};
+
+	if (setGuessedContentType && 0 == EsMemoryCompare(&information.contentType, &zeroIdentifier, sizeof(EsUniqueIdentifier))) {
+		EsUniqueIdentifier identifier = FileTypeMatchByExtension(path);
+
+		if (EsMemoryCompare(&identifier, &zeroIdentifier, sizeof(EsUniqueIdentifier))) {
+			EsFileInformation information = EsFileOpen(STRING(path), ES_FILE_WRITE_SHARED | ES_NODE_FAIL_IF_NOT_FOUND);
+
+			if (information.error == ES_SUCCESS) {
+				EsFileControl(information.handle, ES_FILE_CONTROL_SET_CONTENT_TYPE, &identifier, sizeof(identifier));
+				EsHandleClose(information.handle);
+			}
+		}
+	}
 
 	for (uintptr_t i = 0; i < loadedFolders.Length(); i++) {
 		if (loadedFolders[i]->itemHandler->type != NAMESPACE_HANDLER_FILE_SYSTEM) continue;
diff --git a/apps/file_manager/main.cpp b/apps/file_manager/main.cpp
index f5cdd5c..be0b177 100644
--- a/apps/file_manager/main.cpp
+++ b/apps/file_manager/main.cpp
@@ -53,12 +53,14 @@ const char *errorTypeStrings[] = {
 #define LOAD_FOLDER_NO_FOCUS (1 << 8)
 
 struct FolderEntry {
+	// TODO Can this structure be made smaller?
 	uint16_t handles;
-	bool isFolder, sizeUnknown;
-	uint8_t nameBytes, extensionOffset, internalNameBytes; // 0 -> 256.
+	bool isFolder, sizeUnknown, guessedContentType;
+	uint8_t nameBytes, internalNameBytes; // 0 -> 256.
 	char *name, *internalName;
 	EsFileOffset size, previousSize;
 	uint64_t id;
+	EsUniqueIdentifier contentType;
 
 	inline String GetName() { 
 		return { .text = name, .bytes = nameBytes ?: 256u, .allocated = nameBytes ?: 256u }; 
@@ -67,11 +69,6 @@ struct FolderEntry {
 	inline String GetInternalName() { 
 		return { .text = internalName, .bytes = internalNameBytes ?: 256u, .allocated = internalNameBytes ?: 256u }; 
 	}
-
-	inline String GetExtension() { 
-		uintptr_t offset = extensionOffset ?: 256u;
-		return { .text = name + offset, .bytes = (nameBytes ?: 256u) - offset }; 
-	}
 };
 
 struct ListEntry {
@@ -227,7 +224,7 @@ void InstanceReportError(struct Instance *instance, int error, EsError code);
 bool InstanceLoadFolder(Instance *instance, String path /* takes ownership */, int historyMode = 0);
 void InstanceUpdateStatusString(Instance *instance);
 void InstanceViewSettingsUpdated(Instance *instance);
-void InstanceRefreshViewType(Instance *instance, bool startTransition);
+void InstanceRefreshViewType(Instance *instance);
 void InstanceFolderPathChanged(Instance *instance, bool fromLoadFolder);
 void InstanceAddContents(struct Instance *instance, HashTable *newEntries);
 void InstanceAddSingle(struct Instance *instance, ListEntry newEntry);
@@ -583,6 +580,10 @@ void _start() {
 				StringDestroy(&openDocuments[i]);
 			}
 
+			for (uintptr_t i = 0; i < knownFileTypes.Length(); i++) {
+				knownFileTypes[i].applicationEntries.Free();
+			}
+
 			EsAssert(!instances.Length());
 			EsHeapFree(fileTypesBuffer.out);
 
@@ -608,7 +609,7 @@ void _start() {
 			size_t pathSectionCount = PathCountSections(fullPath);
 
 			for (uintptr_t i = 0; i < pathSectionCount; i++) {
-				FolderFileUpdatedAtPath(PathGetParent(fullPath, i + 1), nullptr);
+				FolderFileUpdatedAtPath(PathGetParent(fullPath, i + 1), nullptr, true);
 			}
 
 			EsHandleClose(message->user.context1.u);
diff --git a/apps/file_manager/type_database.cpp b/apps/file_manager/type_database.cpp
index 9c690fa..f0eb6f5 100644
--- a/apps/file_manager/type_database.cpp
+++ b/apps/file_manager/type_database.cpp
@@ -2,101 +2,242 @@
 // It is released under the terms of the MIT license -- see LICENSE.md.
 // Written by: nakst.
 
+struct FileTypeApplicationEntry {
+	int64_t application;
+	bool open;
+};
+
 struct FileType {
+	Array<FileTypeApplicationEntry> applicationEntries; // One per application that is involved with this type.
+	EsUniqueIdentifier identifier;
 	char *name;
 	size_t nameBytes;
-	char *extension;
-	size_t extensionBytes;
 	uint32_t iconID;
-	int64_t openHandler;
-
-	// TODO Allow applications to register their own thumbnail generators.
-	bool hasThumbnailGenerator;
+	bool textual;
+	bool hasThumbnailGenerator; // TODO Allow applications to register their own thumbnail generators.
 };
 
 Array<FileType> knownFileTypes; 
-HashStore<char, uintptr_t /* index into knownFileTypes */> knownFileTypesByExtension;
+HashStore<char, EsUniqueIdentifier> knownFileTypesByExtension;
 EsBuffer fileTypesBuffer;
 
 void AddKnownFileTypes() {
-#define ADD_FILE_TYPE(_extension, _name, _iconID) \
+#define ADD_FILE_TYPE(_name, _iconID) \
 	{ \
 		FileType type = {}; \
 		type.name = (char *) _name; \
 		type.nameBytes = EsCStringLength(_name); \
-		type.extension = (char *) _extension; \
-		type.extensionBytes = EsCStringLength(_extension); \
 		type.iconID = _iconID; \
 		knownFileTypes.Add(type); \
 	}
 
 #define KNOWN_FILE_TYPE_DIRECTORY (0)
-	ADD_FILE_TYPE("", interfaceString_CommonItemFolder, ES_ICON_FOLDER);
+	ADD_FILE_TYPE(interfaceString_CommonItemFolder, ES_ICON_FOLDER);
 #define KNOWN_FILE_TYPE_UNKNOWN (1)
-	ADD_FILE_TYPE("", interfaceString_CommonItemFile, ES_ICON_UNKNOWN);
+	ADD_FILE_TYPE(interfaceString_CommonItemFile, ES_ICON_UNKNOWN);
 #define KNOWN_FILE_TYPE_DRIVE_HDD (2)
-	ADD_FILE_TYPE("", interfaceString_CommonDriveHDD, ES_ICON_DRIVE_HARDDISK);
+	ADD_FILE_TYPE(interfaceString_CommonDriveHDD, ES_ICON_DRIVE_HARDDISK);
 #define KNOWN_FILE_TYPE_DRIVE_SSD (3)
-	ADD_FILE_TYPE("", interfaceString_CommonDriveSSD, ES_ICON_DRIVE_HARDDISK_SOLIDSTATE);
+	ADD_FILE_TYPE(interfaceString_CommonDriveSSD, ES_ICON_DRIVE_HARDDISK_SOLIDSTATE);
 #define KNOWN_FILE_TYPE_DRIVE_CDROM (4)
-	ADD_FILE_TYPE("", interfaceString_CommonDriveCDROM, ES_ICON_MEDIA_OPTICAL);
+	ADD_FILE_TYPE(interfaceString_CommonDriveCDROM, ES_ICON_MEDIA_OPTICAL);
 #define KNOWN_FILE_TYPE_DRIVE_USB_MASS_STORAGE (5)
-	ADD_FILE_TYPE("", interfaceString_CommonDriveUSBMassStorage, ES_ICON_DRIVE_REMOVABLE_MEDIA_USB);
+	ADD_FILE_TYPE(interfaceString_CommonDriveUSBMassStorage, ES_ICON_DRIVE_REMOVABLE_MEDIA_USB);
 #define KNOWN_FILE_TYPE_DRIVES_PAGE (6)
-	ADD_FILE_TYPE("", interfaceString_FileManagerDrivesPage, ES_ICON_COMPUTER_LAPTOP);
+	ADD_FILE_TYPE(interfaceString_FileManagerDrivesPage, ES_ICON_COMPUTER_LAPTOP);
+#define KNOWN_FILE_TYPE_SPECIAL_COUNT (7)
 
 	fileTypesBuffer = { .canGrow = true };
 	EsSystemConfigurationReadFileTypes(&fileTypesBuffer);
+
 	EsINIState s = { .buffer = (char *) fileTypesBuffer.out, .bytes = fileTypesBuffer.bytes };
 	FileType type = {};
+	FileTypeApplicationEntry applicationEntry = {};
+	bool specifiedTextual = false, specifiedHasThumbnailGenerator = false, hasUUID = false;
+	const char *matchValue;
+	size_t matchValueBytes = 0;
 	
 	while (EsINIParse(&s)) {
 		if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("name"))) {
 			type.name = s.value, type.nameBytes = s.valueBytes;
-		} else if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("extension"))) {
-			type.extension = s.value, type.extensionBytes = s.valueBytes;
-		} else if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("open"))) {
-			type.openHandler = EsIntegerParse(s.value, s.valueBytes);
+		} else if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("uuid"))) {
+			type.identifier = EsUniqueIdentifierParse(s.value, s.valueBytes);
+			hasUUID = true;
 		} else if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("icon"))) {
 			type.iconID = EsIconIDFromString(s.value, s.valueBytes);
-		} else if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("has_thumbnail_generator")) && EsIntegerParse(s.value, s.valueBytes)) {
+		} else if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("has_thumbnail_generator"))) {
 			// TODO Proper thumbnail generator registrations.
-			type.hasThumbnailGenerator = true;
+			type.hasThumbnailGenerator = EsIntegerParse(s.value, s.valueBytes) != 0;
+		} else if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("textual"))) {
+			type.textual = EsIntegerParse(s.value, s.valueBytes) != 0;
+		} else if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("application"))) {
+			applicationEntry.application = EsIntegerParse(s.value, s.valueBytes);
+		} else if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("actions"))) {
+			uintptr_t p = 0, q = 0;
+
+			while (q <= s.valueBytes) {
+				if (q == s.valueBytes || s.value[q] == ',') {
+					String string = StringFromLiteralWithSize(&s.value[p], q - p);
+					p = q + 1;
+
+					if (StringEquals(string, StringFromLiteral("open"))) {
+						applicationEntry.open = true;
+					} else {
+						EsPrint("File Manager: Unknown file type entry action '%s'.\n", STRFMT(string));
+					}
+				}
+
+				q++;
+			}
+		} else if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("match"))) {
+			matchValue = s.value;
+			matchValueBytes = s.valueBytes;
 		}
 
 		if (!EsINIPeek(&s) || !s.keyBytes) {
-			uintptr_t index = knownFileTypes.Length();
-			knownFileTypes.Add(type);
-			*knownFileTypesByExtension.Put(type.extension, type.extensionBytes) = index;
+			EsUniqueIdentifier zeroIdentifier = {};
+
+			if (EsMemoryCompare(&type.identifier, &zeroIdentifier, sizeof(EsUniqueIdentifier))) {
+				bool typeFound = false;
+				uint32_t typeIndex = 0;
+
+				ES_MACRO_SEARCH(knownFileTypes.Length(), { 
+					result = EsMemoryCompare(&type.identifier, &knownFileTypes[index].identifier, sizeof(EsUniqueIdentifier));
+				}, typeIndex, typeFound);
+				
+				EsAssert(typeIndex >= KNOWN_FILE_TYPE_SPECIAL_COUNT);
+				FileType *existing;
+
+				if (!typeFound) {
+					existing = knownFileTypes.Insert(type, typeIndex);
+					EsPrint("File Manager: Type %I registered by application %d with name '%s'.\n",
+							type.identifier, applicationEntry.application, type.nameBytes, type.name);
+				} else {
+					// TODO Priority system.
+					existing = &knownFileTypes[typeIndex];
+					EsAssert(0 == EsMemoryCompare(&existing->identifier, &type.identifier, sizeof(EsUniqueIdentifier)));
+					if (type.nameBytes) existing->name = type.name, existing->nameBytes = type.nameBytes;
+					if (type.iconID) existing->iconID = type.iconID;
+					if (specifiedTextual) existing->textual = type.textual;
+					if (specifiedHasThumbnailGenerator) existing->hasThumbnailGenerator = type.hasThumbnailGenerator;
+					EsPrint("File Manager: Type %I updated by application %d with name '%s'.\n",
+							type.identifier, applicationEntry.application, type.nameBytes, type.name);
+				}
+
+				existing->applicationEntries.Add(applicationEntry);
+
+				if (matchValueBytes) {
+					uintptr_t p = 0, q = 0;
+
+					while (q <= matchValueBytes) {
+						if (q == matchValueBytes || matchValue[q] == ',') {
+							String string = StringFromLiteralWithSize(&matchValue[p], q - p);
+							p = q + 1;
+
+							if (StringStartsWith(string, StringFromLiteral("ext:"))) {
+								String extension = StringSlice(string, 4, -1);
+								bool isLower = true;
+
+								for (uintptr_t i = 0; i < extension.bytes; i++) {
+									if (EsCRTisupper(extension.text[i])) {
+										isLower = false;
+									}
+								}
+
+								if (extension.bytes && isLower) {
+									EsPrint("File Manager: Matching extension '%s' as %I.\n",
+											STRFMT(string), type.identifier);
+									*knownFileTypesByExtension.Put(STRING(extension)) = type.identifier;
+								} else {
+									EsPrint("File Manager: Invalid file type entry extension match '%s'.\n", 
+											STRFMT(string));
+								}
+							} else {
+								EsPrint("File Manager: Unknown file type entry match '%s'.\n", STRFMT(string));
+							}
+						}
+
+						q++;
+					}
+				}
+			} else {
+				// The UUID is invalid, ignore the entry.
+				if (hasUUID) EsPrint("File Manager: Discarding file type entry with invalid UUID.\n");
+			}
+
 			EsMemoryZero(&type, sizeof(type));
+			EsMemoryZero(&applicationEntry, sizeof(applicationEntry));
+			specifiedTextual = false, specifiedHasThumbnailGenerator = false, hasUUID = false;
+			matchValueBytes = 0;
+		}
+	}
+
+	s = { .buffer = (char *) fileTypesBuffer.out, .bytes = fileTypesBuffer.bytes };
+
+	while (EsINIParse(&s)) {
+		if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("application"))) {
+			applicationEntry.application = EsIntegerParse(s.value, s.valueBytes);
+		} else if (0 == EsStringCompareRaw(s.key, s.keyBytes, EsLiteral("opens_any_textual_file"))) {
+			applicationEntry.open = true;
+		}
+
+		if (!EsINIPeek(&s) || !s.keyBytes) {
+			if (applicationEntry.open) {
+				for (uintptr_t i = 0; i < knownFileTypes.Length(); i++) {
+					if (knownFileTypes[i].textual) {
+						knownFileTypes[i].applicationEntries.Insert(applicationEntry, 0);
+						EsPrint("File Manager: Type %I is textual, so application %d can open it.\n", 
+								knownFileTypes[i].identifier, applicationEntry.application);
+					}
+				}
+			}
+
+			EsMemoryZero(&applicationEntry, sizeof(applicationEntry));
 		}
 	}
 }
 
+EsUniqueIdentifier FileTypeMatchByExtension(String name) {
+	String extension = PathGetExtension(name);
+	char buffer[32];
+	uintptr_t i = 0;
+
+	for (; i < extension.bytes && i < 32; i++) {
+		buffer[i] = EsCRTtolower(extension.text[i]);
+	}
+
+	return knownFileTypesByExtension.Get1(buffer, i);
+}
+
 FileType *FolderEntryGetType(Folder *folder, FolderEntry *entry) {
+	EsUniqueIdentifier zeroIdentifier = {};
+
 	if (entry->isFolder) {
 		if (folder->itemHandler->getFileType != NamespaceDefaultGetFileType) {
 			String path = StringAllocateAndFormat("%s%s", STRFMT(folder->path), STRFMT(entry->GetInternalName()));
 			FileType *type = &knownFileTypes[folder->itemHandler->getFileType(path)];
 			StringDestroy(&path);
 			return type;
-		} else {
-			return &knownFileTypes[KNOWN_FILE_TYPE_DIRECTORY];
-		}
-	} else {
-		String extension = entry->GetExtension();
-		char buffer[32];
-		uintptr_t i = 0;
-
-		for (; i < extension.bytes && i < 32; i++) {
-			if (EsCRTisupper(extension.text[i])) {
-				buffer[i] = EsCRTtolower(extension.text[i]);
-			} else {
-				buffer[i] = extension.text[i];
-			}
 		}
 
-		uintptr_t index = knownFileTypesByExtension.Get1(buffer, i);
-		return &knownFileTypes[index ? index : KNOWN_FILE_TYPE_UNKNOWN];
+		return &knownFileTypes[KNOWN_FILE_TYPE_DIRECTORY];
+	} 
+	
+	if (0 == EsMemoryCompare(&entry->contentType, &zeroIdentifier, sizeof(EsUniqueIdentifier))) {
+		entry->contentType = FileTypeMatchByExtension(entry->GetName());
+		entry->guessedContentType = true;
+	} 
+
+	if (0 == EsMemoryCompare(&entry->contentType, &zeroIdentifier, sizeof(EsUniqueIdentifier))) {
+		return &knownFileTypes[KNOWN_FILE_TYPE_UNKNOWN];
 	}
+
+	bool typeFound = false;
+	uint32_t typeIndex = 0;
+
+	ES_MACRO_SEARCH(knownFileTypes.Length(), { 
+		result = EsMemoryCompare(&entry->contentType, &knownFileTypes[index].identifier, sizeof(EsUniqueIdentifier));
+	}, typeIndex, typeFound);
+
+	return &knownFileTypes[typeFound ? typeIndex : KNOWN_FILE_TYPE_UNKNOWN];
 }
diff --git a/apps/file_manager/ui.cpp b/apps/file_manager/ui.cpp
index 516b277..37a0b18 100644
--- a/apps/file_manager/ui.cpp
+++ b/apps/file_manager/ui.cpp
@@ -153,7 +153,7 @@ bool InstanceLoadFolder(Instance *instance, String path /* takes ownership */, i
 			}
 		}
 
-		InstanceRefreshViewType(instance, false);
+		InstanceRefreshViewType(instance);
 
 		// Update the user interface.
 
@@ -168,11 +168,7 @@ bool InstanceLoadFolder(Instance *instance, String path /* takes ownership */, i
 	return true;
 }
 
-void InstanceRefreshViewType(Instance *instance, bool startTransition) {
-	if (startTransition) {
-		EsElementStartTransition(instance->list, ES_TRANSITION_FADE, ES_ELEMENT_TRANSITION_CONTENT_ONLY, 1.0f);
-	}
-
+void InstanceRefreshViewType(Instance *instance) {
 	EsCommandSetCheck(&instance->commandViewDetails,    instance->viewSettings.viewType == VIEW_DETAILS    ? ES_CHECK_CHECKED : ES_CHECK_UNCHECKED, false);
 	EsCommandSetCheck(&instance->commandViewTiles,      instance->viewSettings.viewType == VIEW_TILES      ? ES_CHECK_CHECKED : ES_CHECK_UNCHECKED, false);
 	EsCommandSetCheck(&instance->commandViewThumbnails, instance->viewSettings.viewType == VIEW_THUMBNAILS ? ES_CHECK_CHECKED : ES_CHECK_UNCHECKED, false);
@@ -222,7 +218,11 @@ int InstanceCompareFolderEntries(FolderEntry *left, FolderEntry *right, uint16_t
 		if (sortColumn == COLUMN_NAME) {
 			result = EsStringCompare(STRING(left->GetName()), STRING(right->GetName()));
 		} else if (sortColumn == COLUMN_TYPE) {
-			result = EsStringCompare(STRING(left->GetExtension()), STRING(right->GetExtension()));
+			if (!left->isFolder) {
+				FileType *leftType = FolderEntryGetType(nullptr, left);
+				FileType *rightType = FolderEntryGetType(nullptr, right);
+				result = EsStringCompare(leftType->name, leftType->nameBytes, rightType->name, rightType->nameBytes);
+			}
 		} else if (sortColumn == COLUMN_SIZE) {
 			if (right->size < left->size) result = 1;
 			else if (right->size > left->size) result = -1;
@@ -385,6 +385,8 @@ void InstanceAddContents(Instance *instance, HashTable *newEntries) {
 		EsListViewRemove(instance->list, 0, 0, oldListEntryCount);
 	}
 
+	// TODO Optimize for each sorting mode.
+	// 	For example, sorting by type is pretty bad because it has to lookup file entry types to do each comparison.
 	InstanceSortListContents(instance->listContents.array, instance->listContents.Length(), instance->viewSettings.sortColumn);
 
 	if (instance->listContents.Length()) {
@@ -835,6 +837,8 @@ int ListCallback(EsElement *element, EsMessage *message) {
 
 		if (listEntry) {
 			FolderEntry *entry = listEntry->entry;
+			EsUniqueIdentifier applicationContentType = (EsUniqueIdentifier) {{ 0xBF, 0x88, 0xE4, 0xDD, 0x71, 0xE8, 0x5F, 0xDE, 
+				0x16, 0xC5, 0xAF, 0x33, 0x41, 0xC7, 0xA2, 0x96 }};
 
 			if (entry->isFolder) {
 				String path = instance->folder->itemHandler->getPathForChild(instance->folder, entry);
@@ -850,7 +854,7 @@ int ListCallback(EsElement *element, EsMessage *message) {
 				} else {
 					InstanceLoadFolder(instance, path);
 				}
-			} else if (StringEquals(entry->GetExtension(), StringFromLiteral("esx"))) {
+			} else if (0 == EsMemoryCompare(&entry->contentType, &applicationContentType, sizeof(EsUniqueIdentifier))) {
 				// TODO Temporary.
 				String path = StringAllocateAndFormat("%s%s", STRFMT(instance->folder->path), STRFMT(entry->GetInternalName()));
 
@@ -866,11 +870,18 @@ int ListCallback(EsElement *element, EsMessage *message) {
 				StringDestroy(&path);
 			} else {
 				FileType *fileType = FolderEntryGetType(instance->folder, entry);
+				FileTypeApplicationEntry *typeEntry = nullptr;
 
-				if (fileType->openHandler) {
+				for (uintptr_t i = 0; i < fileType->applicationEntries.Length(); i++) {
+					if (fileType->applicationEntries[i].open) {
+						typeEntry = &fileType->applicationEntries[i];
+					}
+				}
+
+				if (typeEntry) {
 					String path = StringAllocateAndFormat("%s%s", STRFMT(instance->folder->path), STRFMT(entry->GetInternalName()));
 					EsApplicationStartupRequest request = {};
-					request.id = fileType->openHandler;
+					request.id = typeEntry->application;
 					request.filePath = path.text;
 					request.filePathBytes = path.bytes;
 					request.flags = EsKeyboardIsCtrlHeld() || message->chooseItem.source == ES_LIST_VIEW_CHOOSE_ITEM_MIDDLE_CLICK 
diff --git a/apps/font_book.ini b/apps/font_book.ini
index c011979..e329bc2 100644
--- a/apps/font_book.ini
+++ b/apps/font_book.ini
@@ -5,10 +5,10 @@ icon=icon_applications_fonts
 [build]
 source=apps/font_book.cpp
 
-[handler]
-extension=ttf
-action=open
+[file_type]
+actions=open
+uuid=DA-BF-EC-06-31-8A-67-B6-E3-95-BC-D1-92-D2-9A-56
 
-[handler]
-extension=otf
-action=open
+[file_type]
+actions=open
+uuid=E7-2B-BB-E7-FF-75-32-E0-4E-75-41-C0-D2-ED-80-56
diff --git a/apps/image_editor.cpp b/apps/image_editor.cpp
index a3e2530..afd6991 100644
--- a/apps/image_editor.cpp
+++ b/apps/image_editor.cpp
@@ -736,14 +736,27 @@ int InstanceCallback(Instance *instance, EsMessage *message) {
 		EsBuffer buffer = { .out = _buffer, .bytes = _bufferBytes };
 		buffer.fileStore = message->instanceSave.file;
 
+		EsUniqueIdentifier typeJPG = (EsUniqueIdentifier) 
+			{{ 0xD8, 0xC2, 0x13, 0xB0, 0x53, 0x64, 0x82, 0x11, 0x48, 0x7B, 0x5B, 0x64, 0x0F, 0x92, 0xB9, 0x38 }};
+		EsUniqueIdentifier typeBMP = (EsUniqueIdentifier) 
+			{{ 0x40, 0x15, 0xB7, 0x82, 0x99, 0x6D, 0xD5, 0x41, 0x96, 0xD5, 0x3B, 0x6D, 0xA6, 0x5F, 0x07, 0x34 }};
+		EsUniqueIdentifier typeTGA = (EsUniqueIdentifier) 
+			{{ 0x69, 0x62, 0x4E, 0x28, 0xA1, 0xE1, 0x7B, 0x35, 0x64, 0x2E, 0x36, 0x01, 0x65, 0x91, 0xBE, 0xA1 }};
+		EsUniqueIdentifier typePNG = (EsUniqueIdentifier) 
+			{{ 0x59, 0x21, 0x05, 0x4D, 0x34, 0x40, 0xAB, 0x61, 0xEC, 0xF9, 0x7D, 0x5C, 0x6E, 0x04, 0x96, 0xAE }};
+
 		if (0 == EsStringCompare(extension, extensionBytes, EsLiteral("jpg"))
 				|| 0 == EsStringCompare(extension, extensionBytes, EsLiteral("jpeg"))) {
+			EsFileStoreSetContentType(message->instanceSave.file, typeJPG);
 			stbi_write_jpg_to_func(WriteCallback, &buffer, width, height, 4, bits, 90);
 		} else if (0 == EsStringCompare(extension, extensionBytes, EsLiteral("bmp"))) {
+			EsFileStoreSetContentType(message->instanceSave.file, typeBMP);
 			stbi_write_bmp_to_func(WriteCallback, &buffer, width, height, 4, bits);
 		} else if (0 == EsStringCompare(extension, extensionBytes, EsLiteral("tga"))) {
+			EsFileStoreSetContentType(message->instanceSave.file, typeTGA);
 			stbi_write_tga_to_func(WriteCallback, &buffer, width, height, 4, bits);
 		} else {
+			EsFileStoreSetContentType(message->instanceSave.file, typePNG);
 			stbi_write_png_to_func(WriteCallback, &buffer, width, height, 4, bits, stride);
 		}
 
diff --git a/apps/image_editor.ini b/apps/image_editor.ini
index 4c7c1fa..bef533e 100644
--- a/apps/image_editor.ini
+++ b/apps/image_editor.ini
@@ -6,10 +6,18 @@ use_single_process=1
 [build]
 source=apps/image_editor.cpp
 
-[handler]
-extension=jpg
-action=open
+[file_type]
+actions=open
+uuid=D8-C2-13-B0-53-64-82-11-48-7B-5B-64-0F-92-B9-38
 
-[handler]
-extension=png
-action=open
+[file_type]
+actions=open
+uuid=59-21-05-4D-34-40-AB-61-EC-F9-7D-5C-6E-04-96-AE
+
+[file_type]
+actions=open
+uuid=40-15-B7-82-99-6D-D5-41-96-D5-3B-6D-A6-5F-07-34
+
+[file_type]
+actions=open
+uuid=69-62-4E-28-A1-E1-7B-35-64-2E-36-01-65-91-BE-A1
diff --git a/apps/markdown_viewer.ini b/apps/markdown_viewer.ini
index d642b8d..2476fcd 100644
--- a/apps/markdown_viewer.ini
+++ b/apps/markdown_viewer.ini
@@ -7,6 +7,6 @@ hidden=1
 [build]
 source=apps/markdown_viewer.cpp
 
-[handler]
-extension=md
-action=open
+[file_type]
+actions=open
+uuid=B1-C3-9E-56-C9-B0-85-D6-AF-98-12-1C-2E-29-8D-24
diff --git a/apps/text_editor.cpp b/apps/text_editor.cpp
index 7ecc786..34c6f2c 100644
--- a/apps/text_editor.cpp
+++ b/apps/text_editor.cpp
@@ -269,6 +269,23 @@ int InstanceCallback(Instance *instance, EsMessage *message) {
 		size_t byteCount;
 		char *contents = EsTextboxGetContents(instance->textboxDocument, &byteCount);
 		EsFileStoreWriteAll(message->instanceSave.file, contents, byteCount);
+
+		bool fileNameContainsExtension = false;
+
+		for (uintptr_t i = 0; i < (uintptr_t) message->instanceSave.nameOrPathBytes && i < 5; i++) {
+			if (message->instanceSave.nameOrPath[message->instanceSave.nameOrPathBytes - i - 1] == '.') {
+				fileNameContainsExtension = true;
+			}
+		}
+
+		if (fileNameContainsExtension) {
+			// Don't set a content type, it should be matched from the file extension.
+		} else {
+			EsUniqueIdentifier plainText = (EsUniqueIdentifier) 
+				{{ 0x25, 0x65, 0x4C, 0x89, 0xE7, 0x29, 0xEA, 0x9E, 0xB5, 0xBE, 0xB5, 0xCA, 0xA7, 0x60, 0xBD, 0x3D }};
+			EsFileStoreSetContentType(message->instanceSave.file, plainText);
+		}
+
 		EsHeapFree(contents);
 		EsInstanceSaveComplete(instance, message->instanceSave.file, true);
 	} else if (message->type == ES_MSG_INSTANCE_OPEN) {
diff --git a/apps/text_editor.ini b/apps/text_editor.ini
index 4765acc..b9de785 100644
--- a/apps/text_editor.ini
+++ b/apps/text_editor.ini
@@ -3,25 +3,8 @@ name=Text Editor
 icon=icon_accessories_text_editor
 use_single_process=1
 
+[file_type]
+opens_any_textual_file=1
+
 [build]
 source=apps/text_editor.cpp
-
-[handler]
-extension=txt
-action=open
-
-[handler]
-extension=cpp
-action=open
-
-[handler]
-extension=h
-action=open
-
-[handler]
-extension=c
-action=open
-
-[handler]
-extension=ini
-action=open
diff --git a/desktop/api.cpp b/desktop/api.cpp
index f6c7aa1..340bedf 100644
--- a/desktop/api.cpp
+++ b/desktop/api.cpp
@@ -1132,6 +1132,10 @@ EsMessage *EsMessageReceive() {
 			}
 		} else if (type == ES_MSG_INSTANCE_OPEN_DELAYED) {
 			InstanceSendOpenMessage((EsInstance *) message.message._argument, false);
+		} else if (type == ES_MSG_INSTANCE_SAVE_COMPLETE_DELAYED) {
+			char buffer[1];
+			buffer[0] = DESKTOP_MSG_COMPLETE_SAVE;
+			MessageDesktop(buffer, 1, ((EsInstance *) message.message._argument)->window->handle);
 		} else if (type == ES_MSG_PRIMARY_CLIPBOARD_UPDATED) {
 			EsInstance *instance = InstanceFromWindowID(message.message.tabOperation.id);
 			if (instance) UIRefreshPrimaryClipboard(instance->window);
@@ -1237,9 +1241,9 @@ void EsInstanceSaveComplete(EsInstance *instance, EsFileStore *file, bool succes
 	APIInstance *apiInstance = (APIInstance *) instance->_private;
 
 	if (instance) {
-		char buffer[1];
-		buffer[0] = DESKTOP_MSG_COMPLETE_SAVE;
-		MessageDesktop(buffer, 1, instance->window->handle);
+		// HACK Post this message so that our handle to the file is (hopefully) closed first.
+		EsMessage m = { .type = ES_MSG_INSTANCE_SAVE_COMPLETE_DELAYED, ._argument = instance };
+		EsMessagePost(nullptr, &m); 
 
 		if (success) {
 			const char *name;
diff --git a/desktop/desktop.cpp b/desktop/desktop.cpp
index 2af9873..0e82c9a 100644
--- a/desktop/desktop.cpp
+++ b/desktop/desktop.cpp
@@ -98,6 +98,7 @@ struct OpenDocument {
 	size_t pathBytes;
 	char *temporarySavePath;
 	size_t temporarySavePathBytes;
+	EsUniqueIdentifier temporarySavePreviousContentType; // The previous content type. Used as the default if the save operation does not set a new content type. This is useful for text/hex editors, where there is no intrinsic content type.
 	EsHandle readHandle;
 	EsObjectID id;
 	EsObjectID currentWriter;
@@ -2312,6 +2313,11 @@ void ApplicationInstanceRequestSave(ApplicationInstance *instance, const char *n
 		EsHeapFree(document->temporarySavePath);
 		document->temporarySavePath = nullptr;
 
+		if (ES_SUCCESS != EsFileControl(document->readHandle, ES_FILE_CONTROL_GET_CONTENT_TYPE, 
+					&document->temporarySavePreviousContentType, sizeof(EsUniqueIdentifier))) {
+			document->temporarySavePreviousContentType = {};
+		}
+
 		EsHandle fileHandle;
 		m.tabOperation.error = TemporaryFileCreate(&fileHandle, &document->temporarySavePath, &document->temporarySavePathBytes, ES_FILE_WRITE);
 
@@ -2410,6 +2416,22 @@ void ApplicationInstanceCompleteSave(ApplicationInstance *fromInstance) {
 		document->readHandle = file.handle;
 	}
 
+	EsUniqueIdentifier newContentType = {}, zeroContentType = {};
+
+	if (ES_SUCCESS == EsFileControl(document->readHandle, ES_FILE_CONTROL_GET_CONTENT_TYPE, &newContentType, sizeof(EsUniqueIdentifier))) {
+		if (0 == EsMemoryCompare(&newContentType, &zeroContentType, sizeof(EsUniqueIdentifier))
+				&& EsMemoryCompare(&document->temporarySavePreviousContentType, &zeroContentType, sizeof(EsUniqueIdentifier))) {
+			// The application did not set a content type, so use the previous content type of the file.
+			EsFileInformation write = EsFileOpen(document->path, document->pathBytes, ES_FILE_WRITE_SHARED | ES_NODE_FAIL_IF_NOT_FOUND);
+
+			if (write.error == ES_SUCCESS) {
+				EsFileControl(write.handle, ES_FILE_CONTROL_SET_CONTENT_TYPE, 
+						&document->temporarySavePreviousContentType, sizeof(EsUniqueIdentifier));
+				EsHandleClose(write.handle);
+			}
+		}
+	}
+
 	document->currentWriter = 0;
 
 	if (desktop.fileManager && desktop.fileManager->singleProcess) {
diff --git a/desktop/files.cpp b/desktop/files.cpp
index aee47ae..36100c6 100644
--- a/desktop/files.cpp
+++ b/desktop/files.cpp
@@ -95,7 +95,7 @@ EsError EsPathCreate(const char *path, ptrdiff_t pathBytes, EsNodeType type, boo
 	return ES_SUCCESS;
 }
 
-EsError EsFileControl(EsHandle file, EsFileControlOperation operation, const void *data, size_t dataBytes) {
+EsError EsFileControl(EsHandle file, EsFileControlOperation operation, void *data, size_t dataBytes) {
 	return EsSyscall(ES_SYSCALL_FILE_CONTROL, file, operation, (uintptr_t) data, dataBytes);
 }
 
@@ -278,6 +278,21 @@ void *EsFileStoreMap(EsFileStore *file, size_t *fileSize, uint32_t flags) {
 	}
 }
 
+void EsFileStoreSetContentType(EsFileStore *file, EsUniqueIdentifier identifier) {
+	if (file->type == FILE_STORE_HANDLE) {
+		EsFileControl(file->handle, ES_FILE_CONTROL_SET_CONTENT_TYPE, &identifier, sizeof(identifier));
+	} else if (file->type == FILE_STORE_PATH) {
+		EsFileInformation information = EsFileOpen(file->path, file->pathBytes, ES_FILE_WRITE | ES_NODE_CREATE_DIRECTORIES);
+
+		if (information.error == ES_SUCCESS) {
+			EsFileControl(file->handle, ES_FILE_CONTROL_SET_CONTENT_TYPE, &identifier, sizeof(identifier));
+			EsHandleClose(information.handle);
+		}
+	} else {
+		// The file store backend doesn't support this operation.
+	}
+}
+
 EsError MountPointAdd(const char *prefix, size_t prefixBytes, EsHandle base, bool addedByApplication) {
 	EsMutexAcquire(&api.mountPointsMutex);
 	bool duplicate = NodeFindMountPoint(prefix, prefixBytes, nullptr, true);
@@ -545,7 +560,7 @@ EsError EsFileWriteAllGather(const char *filePath, ptrdiff_t filePathLength, con
 		filePathLength = EsCStringLength(filePath);
 	}
 
-	EsFileInformation information = EsFileOpen((char *) filePath, filePathLength, ES_FILE_WRITE | ES_NODE_CREATE_DIRECTORIES);
+	EsFileInformation information = EsFileOpen(filePath, filePathLength, ES_FILE_WRITE | ES_NODE_CREATE_DIRECTORIES);
 
 	if (ES_SUCCESS != information.error) {
 		return information.error;
diff --git a/desktop/os.header b/desktop/os.header
index 05cb15a..e0bc812 100644
--- a/desktop/os.header
+++ b/desktop/os.header
@@ -763,6 +763,7 @@ inttype EsConnectionOpenFlags uint32_t none {
 inttype EsFileControlOperation uint32_t none {
 	ES_FILE_CONTROL_FLUSH = 0 // data/dataBytes ignored
 	ES_FILE_CONTROL_SET_CONTENT_TYPE = 1 // data EsUniqueIdentifier; dataBytes ignored
+	ES_FILE_CONTROL_GET_CONTENT_TYPE = 2 // data EsUniqueIdentifier; dataBytes ignored
 };
 
 inttype EsElementUpdateContentFlags uint32_t none {
@@ -2142,7 +2143,7 @@ function EsError EsFileWriteAllGatherFromHandle(EsHandle handle, const void **da
 function void *EsFileMap(STRING filePath, size_t *fileSize, uint32_t flags) @native();
 function EsError EsFileCopy(STRING source, STRING destination, void **copyBuffer = ES_NULL, EsFileCopyCallback callback = ES_NULL, EsGeneric data = ES_NULL) @todo(); // If you are copying lots of files, you can reuse the temporary copy buffer by storing the output copyBuffer; call EsHeapFree on it after the last copy.
 
-function EsError EsFileControl(EsHandle file, EsFileControlOperation operation, const void *data, size_t dataBytes) @buffer_in(data, dataBytes); 
+function EsError EsFileControl(EsHandle file, EsFileControlOperation operation, void *data, size_t dataBytes) @buffer_out(data, dataBytes); // TODO This annotation is incorrect, it might be in or out depending on the operation.
 function EsFileInformation EsFileOpen(STRING path, EsFileOpenFlags flags);
 function EsFileOffset EsFileGetSize(EsHandle handle);
 function size_t EsFileReadSync(EsHandle file, EsFileOffset offset, size_t size, void *buffer) @buffer_out(buffer, size);
@@ -2162,6 +2163,7 @@ function bool EsFileStoreWriteAll(EsFileStore *file, const void *data, size_t da
 function bool EsFileStoreAppend(EsFileStore *file, const void *data, size_t dataBytes) @buffer_in(data, dataBytes);
 function EsFileOffsetDifference EsFileStoreGetSize(EsFileStore *file); // Returns -1 on error.
 function void *EsFileStoreMap(EsFileStore *file, size_t *fileSize, uint32_t flags) @native();
+function void EsFileStoreSetContentType(EsFileStore *file, EsUniqueIdentifier identifier);
 
 // These calls require permission_all_files.
 function bool EsMountPointGetVolumeInformation(STRING prefix, EsVolumeInformation *information) @out(information); // Returns false if the mount point does not exist.
@@ -2394,6 +2396,7 @@ function bool EsUTF8IsValid(STRING input); // Does not check for surrogate chara
 
 function double EsDoubleParse(STRING string, char **endptr) @native(); 
 function int64_t EsIntegerParse(STRING text); // Parses in hexadecimal if the first two characters are '0x'.
+function EsUniqueIdentifier EsUniqueIdentifierParse(STRING text);
 
 // CRT functions.
 
diff --git a/desktop/prefix.h b/desktop/prefix.h
index 662adcf..41de85e 100644
--- a/desktop/prefix.h
+++ b/desktop/prefix.h
@@ -425,6 +425,7 @@ extern "C" void *EsBufferWrite(EsBuffer *buffer, const void *source, size_t writ
 #define ES_MSG_PING				((EsMessageType) (ES_MSG_SYSTEM_START + 0x203)) /* Sent by Desktop to check processes are processing messages. */
 #define ES_MSG_WAKEUP				((EsMessageType) (ES_MSG_SYSTEM_START + 0x204)) /* Sent to wakeup the message thread, so that it can process locally posted messages. */
 #define ES_MSG_INSTANCE_OPEN_DELAYED		((EsMessageType) (ES_MSG_SYSTEM_START + 0x205))
+#define ES_MSG_INSTANCE_SAVE_COMPLETE_DELAYED   ((EsMessageType) (ES_MSG_SYSTEM_START + 0x206))
 
 #endif
 
diff --git a/desktop/text.cpp b/desktop/text.cpp
index 49ff1c8..28b6106 100644
--- a/desktop/text.cpp
+++ b/desktop/text.cpp
@@ -87,7 +87,7 @@ struct TextPiece {
 	uintptr_t glyphOffset;
 	size_t glyphCount;
 	uintptr_t start, end;
-	bool isTabPiece;
+	bool isTabPiece, isEllipsisPiece;
 };
 
 struct TextLine {
@@ -1829,6 +1829,7 @@ void TextAddEllipsis(EsTextPlan *plan, int32_t maximumLineWidth, bool needFinalE
 		piece.glyphOffset = plan->glyphInfos.Length();
 		piece.ascent  =  FontGetAscent (&plan->font) + plan->currentTextStyle->baselineOffset, 
 		piece.descent = -FontGetDescent(&plan->font) - plan->currentTextStyle->baselineOffset;
+		piece.isEllipsisPiece = true;
 
 		for (uintptr_t i = 0; i < glyphCount; i++) {
 			if (!plan->glyphInfos.Add(glyphInfos[i])) break;
@@ -2295,7 +2296,7 @@ void DrawTextPiece(EsPainter *painter, EsTextPlan *plan, TextPiece *piece, TextL
 
 	// Draw the selection background.
 
-	if (selection->caret0 != selection->caret1 && !selection->hideCaret) {
+	if (selection->caret0 != selection->caret1 && !selection->hideCaret && !piece->isEllipsisPiece) {
 		int sCursorX = cursorX, selectionStartX = -1, selectionEndX = -1;
 
 		for (uintptr_t i = 0; i < piece->glyphCount; i++) {
diff --git a/help/Build System.md b/help/Build System.md
index 6cd7846..131c36d 100644
--- a/help/Build System.md	
+++ b/help/Build System.md	
@@ -97,15 +97,13 @@ In the `[embed]` section there is a list of files that should be embedded into t
 
 Each `[file_type]` section provides information about a file type.
 
-- `extension` Gives the file name extension for the file type.
+- `match` Gives the file name extensions to match for the file type.
 - `name` Gives the readable name of the file type, which will be shown to the user. TODO Translations.
 - `icon` Gives the name of the icon from `desktop/icons.header` to show for files of this type. TODO Bundled icons.
 - `has_thumbnail_generator` Set to 1 if the file type has a thumbnail generator. Only images are supported at the moment. TODO Custom thumbnail generators.
-
-Each `[handler]` section describes this application's support to manage files of a given file type.
-
-- `extension` The file name extension of the file type.
-- `action` The action that this application support for the file type. Currently only "open" is supported.
+- `uuid` The EsUniqueIdentifier of the file type.
+- `textual` Set to 1 if the file type can be read by plain text editors.
+- `actions` The actions the application supports with this file type, e.g. `open`.
 
 ### Standard build configuration options
 
diff --git a/help/Content Types.txt b/help/Content Types.txt
new file mode 100644
index 0000000..a20afa7
--- /dev/null
+++ b/help/Content Types.txt	
@@ -0,0 +1,119 @@
+These are the EsUniqueIdentifier values for different file content types.
+TODO Write up how the content type system works.
+
+ELF executable
+{ 0xAB, 0xDE, 0x98, 0xB5, 0x56, 0x2C, 0x04, 0xDF, 0x1E, 0x43, 0xC8, 0x10, 0x24, 0x63, 0xDB, 0xB8 }
+
+esx application
+{ 0xBF, 0x88, 0xE4, 0xDD, 0x71, 0xE8, 0x5F, 0xDE, 0x16, 0xC5, 0xAF, 0x33, 0x41, 0xC7, 0xA2, 0x96 }
+
+plain text files 
+{ 0x25, 0x65, 0x4C, 0x89, 0xE7, 0x29, 0xEA, 0x9E, 0xB5, 0xBE, 0xB5, 0xCA, 0xA7, 0x60, 0xBD, 0x3D }
+
+bochs config file
+{ 0xFF, 0x92, 0xF0, 0x53, 0x28, 0x83, 0xDC, 0xF1, 0xBA, 0xDD, 0xDE, 0x79, 0x92, 0x33, 0x3F, 0x73 }
+
+build core file
+{ 0x6F, 0x2A, 0x23, 0x16, 0xAF, 0xA3, 0xD0, 0xFB, 0x95, 0x06, 0x52, 0xB3, 0x67, 0xFB, 0x37, 0xFA }
+
+theme designer source file
+{ 0x26, 0x4A, 0xE0, 0x6C, 0x0F, 0xE8, 0x2C, 0xE7, 0xF4, 0x6E, 0x4E, 0x76, 0x5B, 0x4A, 0xCF, 0x4F }
+
+uxn rom
+{ 0x76, 0xC2, 0xC1, 0x73, 0xB1, 0x20, 0x3D, 0x42, 0x70, 0xFD, 0xD4, 0xBD, 0x66, 0xE9, 0x2A, 0x39 }
+
+static library .a
+{ 0x7D, 0x39, 0xBF, 0x18, 0x9E, 0x07, 0xBC, 0xD3, 0x4F, 0x9F, 0x87, 0xEC, 0x6F, 0x70, 0x65, 0x5D }
+
+libtool archive .la
+{ 0x8F, 0x10, 0x4F, 0x33, 0x4A, 0xE5, 0x2D, 0xA7, 0x2A, 0x80, 0x2C, 0x4F, 0xEA, 0xE4, 0x99, 0xB1 }
+
+compiled object .o
+{ 0xB5, 0x19, 0xF2, 0x0D, 0xAD, 0x4F, 0xD4, 0xC9, 0xA4, 0xBF, 0x97, 0xE4, 0x5E, 0x4C, 0x55, 0x00 }
+
+c source file
+{ 0x36, 0x02, 0xD3, 0xAC, 0x6C, 0xDE, 0x8D, 0x31, 0xFA, 0x70, 0xB2, 0xDA, 0xFA, 0x81, 0x53, 0x69 }
+
+c++ source file
+{ 0x35, 0x84, 0xA6, 0x0E, 0x52, 0x28, 0xBA, 0xAB, 0xCA, 0x74, 0x14, 0xF4, 0xE1, 0x15, 0xCA, 0x5F }
+
+c header file
+{ 0xD1, 0x16, 0xC4, 0xC1, 0x7B, 0xC0, 0xED, 0x4F, 0xCA, 0xAC, 0x18, 0x05, 0x32, 0x1D, 0x56, 0x32 }
+
+html file
+{ 0x4A, 0x5A, 0x1C, 0xE5, 0xEE, 0x08, 0x6E, 0x04, 0x13, 0x9C, 0x6D, 0x05, 0x48, 0x5C, 0xE5, 0xD2 }
+
+source template
+{ 0x76, 0x35, 0xF3, 0xF5, 0xC2, 0x69, 0x8A, 0xA4, 0xE4, 0x68, 0x5F, 0xE5, 0x2C, 0x73, 0x10, 0xF9 }
+
+linker script
+{ 0x23, 0x56, 0xBC, 0xD4, 0x5A, 0xD6, 0x56, 0x08, 0x06, 0x61, 0x7C, 0x33, 0x38, 0x66, 0xD5, 0x1F }
+
+markdown
+{ 0xB1, 0xC3, 0x9E, 0x56, 0xC9, 0xB0, 0x85, 0xD6, 0xAF, 0x98, 0x12, 0x1C, 0x2E, 0x29, 0x8D, 0x24 }
+
+UNIX package configuration
+{ 0x74, 0x72, 0x01, 0x17, 0x97, 0x4B, 0x6B, 0x4B, 0x74, 0xCD, 0x18, 0x7C, 0x8F, 0x3C, 0x58, 0xBC }
+
+python script
+{ 0x77, 0x19, 0xBA, 0x87, 0x2E, 0xDB, 0x51, 0xA4, 0x71, 0x5D, 0xFF, 0x8D, 0x39, 0x86, 0x96, 0xF0 }
+
+UNIX manual file
+{ 0xDB, 0x72, 0xDD, 0x5D, 0x92, 0x54, 0x09, 0x1A, 0xC4, 0x16, 0xDD, 0x89, 0x0B, 0x13, 0x12, 0x1F }
+
+application configuration file
+{ 0x18, 0x8D, 0xD3, 0xAC, 0x35, 0xF5, 0xD3, 0x01, 0x8C, 0x66, 0xFD, 0x12, 0xE1, 0xED, 0xE2, 0x6F }
+
+INI configuration file
+{ 0x81, 0x72, 0x43, 0x29, 0xE5, 0x37, 0x89, 0x51, 0x8E, 0x22, 0xA0, 0x67, 0xA5, 0xB9, 0x42, 0x2C }
+
+gzip archive
+{ 0x7D, 0x93, 0x66, 0x74, 0x80, 0x0B, 0x64, 0x9F, 0x16, 0x5D, 0x44, 0xA5, 0x45, 0xFF, 0x80, 0xBF }
+
+virtual drive image
+{ 0xE1, 0x61, 0x4D, 0x0D, 0x32, 0xEC, 0xE0, 0x0F, 0x36, 0x7F, 0xE9, 0x7B, 0x3F, 0x16, 0x43, 0x02 }
+
+jpeg image
+{ 0xD8, 0xC2, 0x13, 0xB0, 0x53, 0x64, 0x82, 0x11, 0x48, 0x7B, 0x5B, 0x64, 0x0F, 0x92, 0xB9, 0x38 }
+
+matroska video
+{ 0x0D, 0xCA, 0x26, 0x92, 0x22, 0x44, 0xEB, 0x6B, 0xC6, 0xE9, 0x6C, 0x8E, 0xFC, 0x28, 0xD2, 0x8E }
+
+3d object .obj
+{ 0xF7, 0x81, 0xE9, 0x21, 0xDF, 0x89, 0x77, 0xD0, 0xC6, 0x97, 0xA8, 0x63, 0xF1, 0xF3, 0x4F, 0x63 }
+
+png image
+{ 0x59, 0x21, 0x05, 0x4D, 0x34, 0x40, 0xAB, 0x61, 0xEC, 0xF9, 0x7D, 0x5C, 0x6E, 0x04, 0x96, 0xAE }
+
+tga image
+{ 0x69, 0x62, 0x4E, 0x28, 0xA1, 0xE1, 0x7B, 0x35, 0x64, 0x2E, 0x36, 0x01, 0x65, 0x91, 0xBE, 0xA1 }
+
+bmp image
+{ 0x40, 0x15, 0xB7, 0x82, 0x99, 0x6D, 0xD5, 0x41, 0x96, 0xD5, 0x3B, 0x6D, 0xA6, 0x5F, 0x07, 0x34 }
+
+truetype font
+{ 0xDA, 0xBF, 0xEC, 0x06, 0x31, 0x8A, 0x67, 0xB6, 0xE3, 0x95, 0xBC, 0xD1, 0x92, 0xD2, 0x9A, 0x56 }
+
+opentype font
+{ 0xE7, 0x2B, 0xBB, 0xE7, 0xFF, 0x75, 0x32, 0xE0, 0x4E, 0x75, 0x41, 0xC0, 0xD2, 0xED, 0x80, 0x56 }
+
+application data
+{ 0xB5, 0x32, 0x22, 0x14, 0x01, 0xCB, 0xD0, 0x1D, 0xA2, 0x55, 0x08, 0xC7, 0x0D, 0x46, 0x86, 0x53 }
+
+bash script
+{ 0x66, 0x42, 0x88, 0xF9, 0xD1, 0x68, 0x47, 0xBF, 0x7F, 0x48, 0x82, 0x77, 0x2B, 0xE3, 0x39, 0xBA }
+
+makefile
+{ 0x3A, 0x58, 0x08, 0x24, 0x00, 0x75, 0xB5, 0x8B, 0xA8, 0x39, 0xD8, 0x37, 0x03, 0x6B, 0x20, 0x85 }
+
+kernel module
+{ 0x80, 0x6D, 0x8E, 0xD6, 0xC7, 0x45, 0xAD, 0xA7, 0x03, 0x5B, 0xB3, 0x64, 0xC5, 0x0A, 0xEE, 0xC6 }
+
+ogg audio
+{ 0xE5, 0x14, 0x14, 0xED, 0x4D, 0x67, 0xC0, 0xD0, 0x62, 0xA1, 0xA4, 0xD4, 0xF5, 0x82, 0xA7, 0x88 }
+
+mp4 video
+{ 0x02, 0x76, 0xE1, 0x41, 0xB8, 0x54, 0x19, 0xA9, 0x05, 0x8D, 0xC1, 0x3F, 0x6E, 0x8F, 0xD7, 0x9E }
+
+wav audio
+{ 0x87, 0xBC, 0xA1, 0xA1, 0x25, 0x76, 0x26, 0x5C, 0x8F, 0x94, 0xD6, 0xD8, 0x35, 0xB6, 0x7A, 0x9F }
diff --git a/kernel/files.cpp b/kernel/files.cpp
index 2b0c629..c6629ac 100644
--- a/kernel/files.cpp
+++ b/kernel/files.cpp
@@ -65,7 +65,7 @@ EsError FSNodeOpenHandle(KNode *node, uint32_t flags, uint8_t mode);
 void FSNodeCloseHandle(KNode *node, uint32_t flags);
 EsError FSNodeDelete(KNode *node);
 EsError FSNodeMove(KNode *node, KNode *destination, const char *newName, size_t nameNameBytes);
-EsError FSFileResize(KNode *node, EsFileOffset newSizeBytes);
+EsError FSFileResize(KNode *node, EsFileOffset newSizeBytes, bool growOnly = false);
 ptrdiff_t FSDirectoryEnumerate(KNode *node, K_USER_BUFFER EsDirectoryChild *buffer, size_t bufferSize);
 EsError FSFileControlFlush(KNode *node);
 EsError FSFileControlSetContentType(KNode *node, EsUniqueIdentifier identifier);
@@ -136,6 +136,7 @@ bool FSCheckPathForIllegalCharacters(const char *path, size_t pathBytes) {
 EsError FSReadIntoCache(CCSpace *fileCache, void *buffer, EsFileOffset offset, EsFileOffset count) {
 	FSFile *node = EsContainerOf(FSFile, cache, fileCache);
 
+	// KWriterLockAssertLocked(&node->resizeLock);
 	KWriterLockTake(&node->writerLock, K_LOCK_SHARED);
 	EsDefer(KWriterLockReturn(&node->writerLock, K_LOCK_SHARED));
 
@@ -238,6 +239,7 @@ EsError FSFileCreateAndResizeOnFileSystem(FSFile *node, EsFileOffset fileSize) {
 EsError FSWriteFromCache(CCSpace *fileCache, const void *buffer, EsFileOffset offset, EsFileOffset count) {
 	FSFile *node = EsContainerOf(FSFile, cache, fileCache);
 
+	// KWriterLockAssertLocked(&node->resizeLock);
 	KWriterLockTake(&node->writerLock, K_LOCK_EXCLUSIVE);
 	EsDefer(KWriterLockReturn(&node->writerLock, K_LOCK_EXCLUSIVE));
 
@@ -335,7 +337,7 @@ void _FSFileResize(FSFile *file, EsFileOffset newSize) {
 	KMutexRelease(&file->fileSystem->moveMutex);
 }
 
-EsError FSFileResize(KNode *node, EsFileOffset newSize) {
+EsError FSFileResize(KNode *node, EsFileOffset newSize, bool growOnly) {
 	if (fs.shutdown) KernelPanic("FSFileResize - Attempting to resize a file after FSShutdown called.\n");
 
 	if (newSize > (EsFileOffset) 1 << 60) {
@@ -350,7 +352,9 @@ EsError FSFileResize(KNode *node, EsFileOffset newSize) {
 	EsError error = ES_SUCCESS;
 	KWriterLockTake(&file->resizeLock, K_LOCK_EXCLUSIVE);
 
-	if (file->blockResize) {
+	if (growOnly && newSize <= file->directoryEntry->totalSize) {
+		// Nothing to do.
+	} else if (file->blockResize) {
 		error = ES_ERROR_OPERATION_BLOCKED;
 	} else if (!file->fileSystem->resize) {
 		error = ES_ERROR_FILE_ON_READ_ONLY_VOLUME;
@@ -365,10 +369,8 @@ EsError FSFileResize(KNode *node, EsFileOffset newSize) {
 ptrdiff_t FSFileWriteSync(KNode *node, K_USER_BUFFER const void *buffer, EsFileOffset offset, EsFileOffset bytes, uint32_t flags) {
 	if (fs.shutdown) KernelPanic("FSFileWriteSync - Attempting to write to a file after FSShutdown called.\n");
 
-	if (offset + bytes > node->directoryEntry->totalSize) {
-		if (ES_SUCCESS != FSFileResize(node, offset + bytes)) {
-			return ES_ERROR_COULD_NOT_RESIZE_FILE;
-		}
+	if (ES_SUCCESS != FSFileResize(node, offset + bytes, true /* growOnly */)) {
+		return ES_ERROR_COULD_NOT_RESIZE_FILE;
 	}
 
 	FSFile *file = (FSFile *) node;
@@ -426,8 +428,10 @@ EsError FSFileControlSetContentType(KNode *node, EsUniqueIdentifier identifier)
 	} else if (~node->fileSystem->flags & ES_VOLUME_STORES_CONTENT_TYPE) {
 		return ES_ERROR_UNSUPPORTED;
 	} else {
+		KWriterLockTake(&node->writerLock, K_LOCK_EXCLUSIVE);
 		node->directoryEntry->contentType = identifier;
 		__sync_fetch_and_or(&node->flags, NODE_MODIFIED); // Set the modified flag *after* making the modification.
+		KWriterLockReturn(&node->writerLock, K_LOCK_EXCLUSIVE);
 		return ES_SUCCESS;
 	}
 }
@@ -1015,9 +1019,11 @@ void FSNodeSynchronize(KNode *node) {
 	if (node->directoryEntry->type == ES_NODE_FILE) {
 		FSFile *file = (FSFile *) node;
 		CCSpaceFlush(&file->cache);
-		KWriterLockTake(&node->writerLock, K_LOCK_EXCLUSIVE);
+		KWriterLockTake(&file->resizeLock, K_LOCK_EXCLUSIVE);
+		KWriterLockTake(&file->writerLock, K_LOCK_EXCLUSIVE);
 		FSFileCreateAndResizeOnFileSystem(file, file->directoryEntry->totalSize);
-		KWriterLockReturn(&node->writerLock, K_LOCK_EXCLUSIVE);
+		KWriterLockReturn(&file->writerLock, K_LOCK_EXCLUSIVE);
+		KWriterLockReturn(&file->resizeLock, K_LOCK_EXCLUSIVE);
 	}
 
 	if (node->flags & NODE_MODIFIED) {
diff --git a/kernel/memory.cpp b/kernel/memory.cpp
index 0f4e094..9f842b2 100644
--- a/kernel/memory.cpp
+++ b/kernel/memory.cpp
@@ -697,10 +697,15 @@ bool MMHandlePageFault(MMSpace *space, uintptr_t address, unsigned faultFlags) {
 			pagesToRead = region->pageCount - (offsetIntoRegion + region->data.file.zeroedBytes) / K_PAGE_SIZE;
 		}
 
+		// This shouldn't block, because mapped files cannot be resized.
+		KWriterLockTake(&region->data.file.node->resizeLock, K_LOCK_SHARED);
+
 		EsError error = CCSpaceAccess(&region->data.file.node->cache, (void *) address, 
 				offsetIntoRegion + region->data.file.offset, pagesToRead * K_PAGE_SIZE, 
 				CC_ACCESS_MAP, space, flags);
 
+		KWriterLockReturn(&region->data.file.node->resizeLock, K_LOCK_SHARED);
+
 		KMutexAcquire(&region->data.mapMutex);
 
 		if (error != ES_SUCCESS) {
diff --git a/kernel/syscall.cpp b/kernel/syscall.cpp
index 33e9e70..3c2f661 100644
--- a/kernel/syscall.cpp
+++ b/kernel/syscall.cpp
@@ -1193,18 +1193,38 @@ SYSCALL_IMPLEMENT(ES_SYSCALL_FILE_CONTROL) {
 
 	if (file->directoryEntry->type != ES_NODE_FILE) {
 		SYSCALL_RETURN(ES_FATAL_ERROR_INCORRECT_NODE_TYPE, true);
-	} else if ((handle.flags & (ES_FILE_WRITE_SHARED | ES_FILE_WRITE)) == 0) {
-		SYSCALL_RETURN(ES_FATAL_ERROR_INCORRECT_FILE_ACCESS, true);
 	}
 
 	EsError error = ES_ERROR_UNSUPPORTED;
 
 	if (argument1 == ES_FILE_CONTROL_FLUSH) {
+		if ((handle.flags & (ES_FILE_WRITE_SHARED | ES_FILE_WRITE)) == 0) {
+			SYSCALL_RETURN(ES_FATAL_ERROR_INCORRECT_FILE_ACCESS, true);
+		}
+
 		error = FSFileControlFlush(file);
 	} else if (argument1 == ES_FILE_CONTROL_SET_CONTENT_TYPE) {
+		if ((handle.flags & (ES_FILE_WRITE_SHARED | ES_FILE_WRITE)) == 0) {
+			SYSCALL_RETURN(ES_FATAL_ERROR_INCORRECT_FILE_ACCESS, true);
+		}
+
 		EsUniqueIdentifier identifier;
 		SYSCALL_READ(&identifier, argument2, sizeof(identifier));
 		error = FSFileControlSetContentType(file, identifier);
+	} else if (argument1 == ES_FILE_CONTROL_GET_CONTENT_TYPE) {
+		EsUniqueIdentifier identifier;
+		KWriterLockTake(&file->writerLock, K_LOCK_SHARED);
+
+		if (file->fileSystem->flags & ES_VOLUME_STORES_CONTENT_TYPE) {
+			identifier = file->directoryEntry->contentType;
+			error = ES_SUCCESS;
+		}
+
+		KWriterLockReturn(&file->writerLock, K_LOCK_SHARED);
+
+		if (error == ES_SUCCESS) {
+			SYSCALL_WRITE(argument2, &identifier, sizeof(EsUniqueIdentifier));
+		}
 	}
 
 	SYSCALL_RETURN(error, false);
diff --git a/ports/bochs/bochs.ini b/ports/bochs/bochs.ini
index a33cfbd..0aaf507 100644
--- a/ports/bochs/bochs.ini
+++ b/ports/bochs/bochs.ini
@@ -9,10 +9,9 @@ custom_compile_command=cp root/Applications/POSIX/bin/bochs bin/Bochs
 require=root/Applications/POSIX/bin/bochs
 
 [file_type]
-extension=bochsrc
+match=ext:bochsrc
 name=Bochs configuration
 icon=icon_applications_development
-
-[handler]
-extension=bochsrc
-action=open
+uuid=FF-92-F0-53-28-83-DC-F1-BA-DD-DE-79-92-33-3F-73
+actions=open
+textual=1
diff --git a/ports/mesa/obj_viewer.ini b/ports/mesa/obj_viewer.ini
index 38fc3ee..6086511 100644
--- a/ports/mesa/obj_viewer.ini
+++ b/ports/mesa/obj_viewer.ini
@@ -9,11 +9,10 @@ link_flags=-lOSMesa -lstdc++ -lz
 with_cstdlib=1
 source=ports/mesa/obj_viewer.c
 
-[handler]
-extension=obj
-action=open
-
 [file_type]
-extension=obj
+match=ext:obj
 name=3D model
 icon=icon_model
+uuid=F7-81-E9-21-DF-89-77-D0-C6-97-A8-63-F1-F3-4F-63
+actions=open
+textual=1
diff --git a/ports/uxn/emulator.ini b/ports/uxn/emulator.ini
index bff167c..3e151ee 100644
--- a/ports/uxn/emulator.ini
+++ b/ports/uxn/emulator.ini
@@ -6,11 +6,9 @@ hidden=1
 source=ports/uxn/emulator.c
 compile_flags=-Wno-unknown-pragmas -Wno-unused-parameter
 
-[handler]
-extension=uxn
-action=open
-
 [file_type]
-extension=uxn
+match=ext:uxn
 name=Uxn ROM
 icon=icon_unknown
+uuid=76-C2-C1-73-B1-20-3D-42-70-FD-D4-BD-66-E9-2A-39
+actions=open
diff --git a/shared/common.cpp b/shared/common.cpp
index dd19b92..341c5e2 100644
--- a/shared/common.cpp
+++ b/shared/common.cpp
@@ -589,6 +589,16 @@ void _StringFormat(FormatCallback callback, void *callbackData, const char *form
 					callback('}', callbackData);
 				} break;
 
+				case 'I': {
+					EsUniqueIdentifier value = va_arg(arguments, EsUniqueIdentifier);
+
+					for (uintptr_t i = 0; i < 16; i++) {
+						if (i) callback('-', callbackData);
+						callback(hexChars[(value.d[i] & 0xF0) >> 4], callbackData);
+						callback(hexChars[(value.d[i] & 0xF)], callbackData);
+					}
+				} break;
+
 				case 'X': {
 					uintptr_t value = va_arg(arguments, uintptr_t);
 					callback(hexChars[(value & 0xF0) >> 4], callbackData);
@@ -920,6 +930,7 @@ int64_t EsStringParseInteger(const char **string, size_t *length, int base) {
 int EsStringCompareRaw(const char *s1, ptrdiff_t length1, const char *s2, ptrdiff_t length2) {
 	if (length1 == -1) length1 = EsCStringLength(s1);
 	if (length2 == -1) length2 = EsCStringLength(s2);
+	if (s1 == s2 && length1 == length2) return 0;
 
 	while (length1 || length2) {
 		if (!length1) return -1;
@@ -945,6 +956,7 @@ int EsStringCompare(const char *s1, ptrdiff_t _length1, const char *s2, ptrdiff_
 	if (_length1 == -1) _length1 = EsCStringLength(s1);
 	if (_length2 == -1) _length2 = EsCStringLength(s2);
 	size_t length1 = _length1, length2 = _length2;
+	if (s1 == s2 && length1 == length2) return 0;
 
 	while (length1 || length2) {
 		if (!length1) return -1;
@@ -1072,6 +1084,28 @@ static int64_t ConvertCharacterToDigit(int character, int base) {
 	return result;
 }
 
+EsUniqueIdentifier EsUniqueIdentifierParse(const char *text, ptrdiff_t bytes) {
+	if (bytes == -1) bytes = EsCStringLength(text);
+	if (bytes != 3 * 16 - 1) return {};
+
+	for (uintptr_t i = 0; i < 15; i++) {
+		if (text[i * 3 + 2] != '-') {
+			return {};
+		}
+	}
+
+	EsUniqueIdentifier identifier;
+
+	for (uintptr_t i = 0; i < 16; i++) {
+		int64_t a = ConvertCharacterToDigit(text[i * 3 + 0], 16);
+		int64_t b = ConvertCharacterToDigit(text[i * 3 + 1], 16);
+		if (a == -1 || b == -1) return {};
+		identifier.d[i] = a * 16 + b;
+	}
+
+	return identifier;
+}
+
 int64_t EsIntegerParse(const char *text, ptrdiff_t bytes) {
 	if (bytes == -1) bytes = EsCStringLength(text);
 
diff --git a/shared/esfs2.h b/shared/esfs2.h
index 1bb8373..de188a2 100644
--- a/shared/esfs2.h
+++ b/shared/esfs2.h
@@ -694,12 +694,13 @@ void PrintTree(uint64_t block, int indent = 2, uint64_t lowerThan = -1) {
 }
 #endif
 
-void NewDirectoryEntry(DirectoryEntry *entry, uint8_t nodeType, EsUniqueIdentifier parentUID, const char *name) {
+void NewDirectoryEntry(DirectoryEntry *entry, uint8_t nodeType, EsUniqueIdentifier parentUID, const char *name, EsUniqueIdentifier contentType) {
 	memcpy(entry->signature, ESFS_DIRECTORY_ENTRY_SIGNATURE, 8);
 	GenerateUniqueIdentifier(&entry->identifier, false);
 	entry->attributeOffset = ESFS_ATTRIBUTE_OFFSET;
 	entry->nodeType = nodeType; 
 	entry->parent = parentUID;
+	entry->contentType = contentType;
 
 	uint8_t *position = (uint8_t *) entry + entry->attributeOffset;
 	size_t newFilenameSize = ((strlen(name) + ESFS_FILENAME_HEADER_SIZE - 1) & ~7) + 8; // Size of name + size of header, rounded up to the nearest 8 bytes.
@@ -736,7 +737,7 @@ void NewDirectoryEntry(DirectoryEntry *entry, uint8_t nodeType, EsUniqueIdentifi
 }
 
 bool AddNode(const char *name, uint8_t nodeType, DirectoryEntry *outputEntry, DirectoryEntryReference *outputReference, 
-		DirectoryEntryReference directoryReference) {
+		DirectoryEntryReference directoryReference, EsUniqueIdentifier contentType) {
 	// Log("add %s to %s\n", name, path);
 
 	// Step 1: Resize the directory so that it can fit another directory entry.
@@ -770,7 +771,7 @@ bool AddNode(const char *name, uint8_t nodeType, DirectoryEntry *outputEntry, Di
 	DirectoryEntry entry = {};
 
 	{
-		NewDirectoryEntry(&entry, nodeType, directory.identifier, name);
+		NewDirectoryEntry(&entry, nodeType, directory.identifier, name, contentType);
 		// Log("\tchild nodes: %ld\n", directoryAttribute->childNodes);
 
 		if (!AccessNode(&directory, &entry, (directoryAttribute->childNodes - 1) * sizeof(DirectoryEntry), sizeof(DirectoryEntry), &reference, false)) {
@@ -1041,6 +1042,7 @@ typedef struct ImportNode {
 	const char *name, *path;
 	struct ImportNode *children;
 	bool isFile;
+	EsUniqueIdentifier contentType;
 } ImportNode;
 
 int64_t Import(ImportNode node, DirectoryEntryReference parentDirectory) {
@@ -1059,7 +1061,7 @@ int64_t Import(ImportNode node, DirectoryEntryReference parentDirectory) {
 				DirectoryEntryReference reference;
 				DirectoryEntry entry;
 
-				if (!AddNode(node.children[i].name, ESFS_NODE_TYPE_FILE, &entry, &reference, parentDirectory)) {
+				if (!AddNode(node.children[i].name, ESFS_NODE_TYPE_FILE, &entry, &reference, parentDirectory, node.children[i].contentType)) {
 					return -1;
 				}
 
@@ -1081,7 +1083,7 @@ int64_t Import(ImportNode node, DirectoryEntryReference parentDirectory) {
 			}
 		} else {
 			DirectoryEntryReference reference;
-			if (!AddNode(node.children[i].name, ESFS_NODE_TYPE_DIRECTORY, NULL, &reference, parentDirectory)) return -1;
+			if (!AddNode(node.children[i].name, ESFS_NODE_TYPE_DIRECTORY, NULL, &reference, parentDirectory, node.children[i].contentType)) return -1;
 			int64_t size = Import(node.children[i], reference);
 			if (size == -1) return -1;
 			DirectoryEntry directory; 
@@ -1241,7 +1243,8 @@ bool Format(uint64_t driveSize, const char *volumeName, EsUniqueIdentifier osIns
 		DirectoryEntry entry;
 		EsUniqueIdentifier unused = {};
 
-		NewDirectoryEntry(&entry, ESFS_NODE_TYPE_FILE, unused, "Kernel");
+		EsUniqueIdentifier elf = (EsUniqueIdentifier) {{ 0xAB, 0xDE, 0x98, 0xB5, 0x56, 0x2C, 0x04, 0xDF, 0x1E, 0x43, 0xC8, 0x10, 0x24, 0x63, 0xDB, 0xB8 }};
+		NewDirectoryEntry(&entry, ESFS_NODE_TYPE_FILE, unused, "Kernel", elf);
 
 		if (WriteDirectoryEntryReference(reference, &entry)) {
 			if (ResizeNode(&entry, kernelBytes)) {
diff --git a/start.sh b/start.sh
index 5e74063..ce33daf 100755
--- a/start.sh
+++ b/start.sh
@@ -1 +1 @@
-cd "$(dirname "$0")" && mkdir -p bin && gcc -o bin/script util/script.c -g -Wall -Wextra -O2 -pthread -ldl && bin/script util/start.script options="`echo $@`"
+cd "$(dirname "$0")" && mkdir -p bin && gcc -o bin/script util/script.c -g -Wall -Wextra -O2 -pthread && bin/script util/start.script options="`echo $@`"
diff --git a/util/api_table.ini b/util/api_table.ini
index 256ec74..00a5423 100644
--- a/util/api_table.ini
+++ b/util/api_table.ini
@@ -37,6 +37,7 @@ EsCommandSetCheck=35
 EsTextboxGetContentsAsDouble=36
 EsFileStoreAppend=37
 EsBufferFlushToFileStore=38
+EsFileStoreSetContentType=39
 EsPathExists=40
 EsInstanceSetClassViewer=41
 EsPathDelete=42
@@ -494,3 +495,4 @@ EsRectangleContainsAll=493
 EsListViewFixedItemSetEnumStringsForColumn=494
 EsImageDisplayGetImageHeight=495
 EsDirectoryEnumerate=496
+EsUniqueIdentifierParse=497
diff --git a/util/build_core.c b/util/build_core.c
index 0a8372d..9d9eed4 100644
--- a/util/build_core.c
+++ b/util/build_core.c
@@ -406,6 +406,91 @@ bool FileExists(const char *path) {
 #endif
 }
 
+#ifndef OS_ESSENCE
+EsUniqueIdentifier MatchFileContentType(const char *pathBuffer) {
+	FILE *f = fopen(pathBuffer, "rb");
+	assert(f);
+	uint32_t elfSignature;
+	fread(&elfSignature, 1, sizeof(elfSignature), f);
+	bool isELFExecutable = elfSignature == 0x464C457F;
+	fclose(f);
+
+	EsUniqueIdentifier t = { 0 };
+
+#define ENDS_WITH(s) (strlen(pathBuffer) >= strlen(s) && 0 == strcmp(pathBuffer + strlen(pathBuffer) - strlen(s), s))
+#define STARTS_WITH(s) (strlen(pathBuffer) >= strlen(s) && 0 == memcmp(pathBuffer, s, strlen(s)))
+	if (ENDS_WITH(".bochsrc"))
+		t = (EsUniqueIdentifier) {{ 0xFF, 0x92, 0xF0, 0x53, 0x28, 0x83, 0xDC, 0xF1, 0xBA, 0xDD, 0xDE, 0x79, 0x92, 0x33, 0x3F, 0x73 }};
+	else if (ENDS_WITH(".build_core"))
+		t = (EsUniqueIdentifier) {{ 0x6F, 0x2A, 0x23, 0x16, 0xAF, 0xA3, 0xD0, 0xFB, 0x95, 0x06, 0x52, 0xB3, 0x67, 0xFB, 0x37, 0xFA }};
+	else if (ENDS_WITH(".designer"))
+		t = (EsUniqueIdentifier) {{ 0x26, 0x4A, 0xE0, 0x6C, 0x0F, 0xE8, 0x2C, 0xE7, 0xF4, 0x6E, 0x4E, 0x76, 0x5B, 0x4A, 0xCF, 0x4F }};
+	else if (ENDS_WITH(".uxn"))
+		t = (EsUniqueIdentifier) {{ 0x76, 0xC2, 0xC1, 0x73, 0xB1, 0x20, 0x3D, 0x42, 0x70, 0xFD, 0xD4, 0xBD, 0x66, 0xE9, 0x2A, 0x39 }};
+	else if (ENDS_WITH(".a"))
+		t = (EsUniqueIdentifier) {{ 0x7D, 0x39, 0xBF, 0x18, 0x9E, 0x07, 0xBC, 0xD3, 0x4F, 0x9F, 0x87, 0xEC, 0x6F, 0x70, 0x65, 0x5D }};
+	else if (ENDS_WITH(".la"))
+		t = (EsUniqueIdentifier) {{ 0x8F, 0x10, 0x4F, 0x33, 0x4A, 0xE5, 0x2D, 0xA7, 0x2A, 0x80, 0x2C, 0x4F, 0xEA, 0xE4, 0x99, 0xB1 }};
+	else if (ENDS_WITH(".esx"))
+		t = (EsUniqueIdentifier) {{ 0xBF, 0x88, 0xE4, 0xDD, 0x71, 0xE8, 0x5F, 0xDE, 0x16, 0xC5, 0xAF, 0x33, 0x41, 0xC7, 0xA2, 0x96 }};
+	else if (ENDS_WITH(".o"))
+		t = (EsUniqueIdentifier) {{ 0xB5, 0x19, 0xF2, 0x0D, 0xAD, 0x4F, 0xD4, 0xC9, 0xA4, 0xBF, 0x97, 0xE4, 0x5E, 0x4C, 0x55, 0x00 }};
+	else if (ENDS_WITH(".c"))
+		t = (EsUniqueIdentifier) {{ 0x36, 0x02, 0xD3, 0xAC, 0x6C, 0xDE, 0x8D, 0x31, 0xFA, 0x70, 0xB2, 0xDA, 0xFA, 0x81, 0x53, 0x69 }};
+	else if (ENDS_WITH(".cpp"))
+		t = (EsUniqueIdentifier) {{ 0x35, 0x84, 0xA6, 0x0E, 0x52, 0x28, 0xBA, 0xAB, 0xCA, 0x74, 0x14, 0xF4, 0xE1, 0x15, 0xCA, 0x5F }};
+	else if (ENDS_WITH(".h"))
+		t = (EsUniqueIdentifier) {{ 0xD1, 0x16, 0xC4, 0xC1, 0x7B, 0xC0, 0xED, 0x4F, 0xCA, 0xAC, 0x18, 0x05, 0x32, 0x1D, 0x56, 0x32 }};
+	else if (ENDS_WITH(".html"))
+		t = (EsUniqueIdentifier) {{ 0x4A, 0x5A, 0x1C, 0xE5, 0xEE, 0x08, 0x6E, 0x04, 0x13, 0x9C, 0x6D, 0x05, 0x48, 0x5C, 0xE5, 0xD2 }};
+	else if (ENDS_WITH(".in"))
+		t = (EsUniqueIdentifier) {{ 0x76, 0x35, 0xF3, 0xF5, 0xC2, 0x69, 0x8A, 0xA4, 0xE4, 0x68, 0x5F, 0xE5, 0x2C, 0x73, 0x10, 0xF9 }};
+	else if (ENDS_WITH("/Makefile"))
+		t = (EsUniqueIdentifier) {{ 0x3A, 0x58, 0x08, 0x24, 0x00, 0x75, 0xB5, 0x8B, 0xA8, 0x39, 0xD8, 0x37, 0x03, 0x6B, 0x20, 0x85 }};
+	else if (ENDS_WITH(".ld") || STARTS_WITH("root/Applications/POSIX/x86_64-essence/lib/ldscripts/"))
+		t = (EsUniqueIdentifier) {{ 0x23, 0x56, 0xBC, 0xD4, 0x5A, 0xD6, 0x56, 0x08, 0x06, 0x61, 0x7C, 0x33, 0x38, 0x66, 0xD5, 0x1F }};
+	else if (ENDS_WITH(".md"))
+		t = (EsUniqueIdentifier) {{ 0xB1, 0xC3, 0x9E, 0x56, 0xC9, 0xB0, 0x85, 0xD6, 0xAF, 0x98, 0x12, 0x1C, 0x2E, 0x29, 0x8D, 0x24 }};
+	else if (ENDS_WITH(".pc"))
+		t = (EsUniqueIdentifier) {{ 0x74, 0x72, 0x01, 0x17, 0x97, 0x4B, 0x6B, 0x4B, 0x74, 0xCD, 0x18, 0x7C, 0x8F, 0x3C, 0x58, 0xBC }};
+	else if (ENDS_WITH(".py"))
+		t = (EsUniqueIdentifier) {{ 0x77, 0x19, 0xBA, 0x87, 0x2E, 0xDB, 0x51, 0xA4, 0x71, 0x5D, 0xFF, 0x8D, 0x39, 0x86, 0x96, 0xF0 }};
+	else if (ENDS_WITH(".sh"))
+		t = (EsUniqueIdentifier) {{ 0x66, 0x42, 0x88, 0xF9, 0xD1, 0x68, 0x47, 0xBF, 0x7F, 0x48, 0x82, 0x77, 0x2B, 0xE3, 0x39, 0xBA }};
+	else if (ENDS_WITH(".txt") || ENDS_WITH("/README") || ENDS_WITH("/LICENSE") || ENDS_WITH("/COPYING") || ENDS_WITH("/AUTHORS") || ENDS_WITH("/TODO")
+		|| ENDS_WITH("/BUGS") || ENDS_WITH("/NEWS") || ENDS_WITH("/CHANGES") || ENDS_WITH("/ReadMe") || ENDS_WITH(".LESSER"))
+			t = (EsUniqueIdentifier) {{ 0x25, 0x65, 0x4C, 0x89, 0xE7, 0x29, 0xEA, 0x9E, 0xB5, 0xBE, 0xB5, 0xCA, 0xA7, 0x60, 0xBD, 0x3D }};
+	else if (ENDS_WITH(".1") || ENDS_WITH(".7") || ENDS_WITH(".info") || ENDS_WITH(".info-1") || ENDS_WITH(".info-2"))
+		t = (EsUniqueIdentifier) {{ 0xDB, 0x72, 0xDD, 0x5D, 0x92, 0x54, 0x09, 0x1A, 0xC4, 0x16, 0xDD, 0x89, 0x0B, 0x13, 0x12, 0x1F }};
+	else if (ENDS_WITH(".conf") || ENDS_WITH(".bfd"))
+		t = (EsUniqueIdentifier) {{ 0x18, 0x8D, 0xD3, 0xAC, 0x35, 0xF5, 0xD3, 0x01, 0x8C, 0x66, 0xFD, 0x12, 0xE1, 0xED, 0xE2, 0x6F }};
+	else if (ENDS_WITH(".ini"))
+		t = (EsUniqueIdentifier) {{ 0x81, 0x72, 0x43, 0x29, 0xE5, 0x37, 0x89, 0x51, 0x8E, 0x22, 0xA0, 0x67, 0xA5, 0xB9, 0x42, 0x2C }};
+	else if (ENDS_WITH(".gz"))
+		t = (EsUniqueIdentifier) {{ 0x7D, 0x93, 0x66, 0x74, 0x80, 0x0B, 0x64, 0x9F, 0x16, 0x5D, 0x44, 0xA5, 0x45, 0xFF, 0x80, 0xBF }};
+	else if (ENDS_WITH(".img"))
+		t = (EsUniqueIdentifier) {{ 0xE1, 0x61, 0x4D, 0x0D, 0x32, 0xEC, 0xE0, 0x0F, 0x36, 0x7F, 0xE9, 0x7B, 0x3F, 0x16, 0x43, 0x02 }};
+	else if (ENDS_WITH(".jpg"))
+		t = (EsUniqueIdentifier) {{ 0xD8, 0xC2, 0x13, 0xB0, 0x53, 0x64, 0x82, 0x11, 0x48, 0x7B, 0x5B, 0x64, 0x0F, 0x92, 0xB9, 0x38 }};
+	else if (ENDS_WITH(".mkv"))
+		t = (EsUniqueIdentifier) {{ 0x0D, 0xCA, 0x26, 0x92, 0x22, 0x44, 0xEB, 0x6B, 0xC6, 0xE9, 0x6C, 0x8E, 0xFC, 0x28, 0xD2, 0x8E }};
+	else if (ENDS_WITH(".obj"))
+		t = (EsUniqueIdentifier) {{ 0xF7, 0x81, 0xE9, 0x21, 0xDF, 0x89, 0x77, 0xD0, 0xC6, 0x97, 0xA8, 0x63, 0xF1, 0xF3, 0x4F, 0x63 }};
+	else if (ENDS_WITH(".png"))
+		t = (EsUniqueIdentifier) {{ 0x59, 0x21, 0x05, 0x4D, 0x34, 0x40, 0xAB, 0x61, 0xEC, 0xF9, 0x7D, 0x5C, 0x6E, 0x04, 0x96, 0xAE }};
+	else if (ENDS_WITH(".ttf"))
+		t = (EsUniqueIdentifier) {{ 0xDA, 0xBF, 0xEC, 0x06, 0x31, 0x8A, 0x67, 0xB6, 0xE3, 0x95, 0xBC, 0xD1, 0x92, 0xD2, 0x9A, 0x56 }};
+	else if (STARTS_WITH("root/Applications/POSIX/share/bochs/"))
+		t = (EsUniqueIdentifier) {{ 0xB5, 0x32, 0x22, 0x14, 0x01, 0xCB, 0xD0, 0x1D, 0xA2, 0x55, 0x08, 0xC7, 0x0D, 0x46, 0x86, 0x53 }};
+	else if (isELFExecutable)
+		t = (EsUniqueIdentifier) {{ 0xAB, 0xDE, 0x98, 0xB5, 0x56, 0x2C, 0x04, 0xDF, 0x1E, 0x43, 0xC8, 0x10, 0x24, 0x63, 0xDB, 0xB8 }};
+#undef ENDS_WITH
+#undef STARTS_WITH
+
+	return t;
+}
+#endif
+
 void CreateImportNode(const char *path, ImportNode *node) {
 	char pathBuffer[256];
 
@@ -429,6 +514,7 @@ void CreateImportNode(const char *path, ImportNode *node) {
 			CreateImportNode(pathBuffer, &child);
 		} else {
 			child.isFile = true;
+			child.contentType = children[i].contentType;
 		}
 
 		child.name = EsStringAllocateAndFormat(NULL, "%s", children[i].nameBytes, children[i].name);
@@ -464,6 +550,7 @@ void CreateImportNode(const char *path, ImportNode *node) {
 			continue;
 		} else {
 			child.isFile = true;
+			child.contentType = MatchFileContentType(pathBuffer);
 		}
 
 		child.name = strdup(dir->d_name);
@@ -549,20 +636,6 @@ bool MakeBundle(const char *outputFile, BundleInput *inputFiles, size_t inputFil
 
 //////////////////////////////////
 
-typedef struct FileType {
-	const char *extension;
-	const char *name;
-	const char *icon;
-	int id, openID;
-	bool hasThumbnailGenerator;
-} FileType;
-
-typedef struct Handler {
-	const char *extension;
-	const char *action;
-	int fileTypeID;
-} Handler;
-
 typedef struct DependencyFile {
 	char path[256];
 	const char *name;
@@ -573,11 +646,9 @@ typedef struct Application {
 
 	const char *name; 
 	EsINIState *properties;
+	EsINIState *fileTypeLines;
 	int id;
 
-	FileType *fileTypes;
-	Handler *handlers;
-
 	bool install, builtin, withCStdLib;
 
 	const char **sources;
@@ -794,8 +865,6 @@ void ParseApplicationManifest(const char *manifestPath) {
 	application.manifestPath = manifestPath;
 	application.compileFlags = "";
 	application.linkFlags = "";
-	Handler *handler = NULL;
-	FileType *fileType = NULL;
 
 	while (EsINIParse(&s)) {
 		EsINIZeroTerminate(&s);
@@ -815,27 +884,8 @@ void ParseApplicationManifest(const char *manifestPath) {
 			else INI_READ_BOOL(disabled, disabled);
 			else INI_READ_BOOL(needs_native_toolchain, needsNativeToolchain);
 			else if (s.keyBytes && s.valueBytes) arrput(application.properties, s);
-		} else if (0 == strcmp(s.section, "handler")) {
-			if (!s.keyBytes) {
-				Handler _handler = {};
-				arrput(application.handlers, _handler);
-				handler = &arrlast(application.handlers);
-			}
-
-			INI_READ_STRING_PTR(extension, handler->extension);
-			INI_READ_STRING_PTR(action, handler->action);
 		} else if (0 == strcmp(s.section, "file_type")) {
-			if (!s.keyBytes) {
-				FileType _fileType = {};
-				_fileType.id = nextID++;
-				arrput(application.fileTypes, _fileType);
-				fileType = &arrlast(application.fileTypes);
-			}
-
-			INI_READ_STRING_PTR(extension, fileType->extension);
-			INI_READ_STRING_PTR(name, fileType->name);
-			INI_READ_STRING_PTR(icon, fileType->icon);
-			INI_READ_BOOL(has_thumbnail_generator, fileType->hasThumbnailGenerator);
+			arrput(application.fileTypeLines, s);
 		} else if (0 == strcmp(s.section, "embed") && s.key[0] != ';' && s.value[0]) {
 			BundleInput input = { 0 };
 			input.path = s.value;
@@ -884,38 +934,6 @@ void OutputSystemConfiguration() {
 		FileWrite(file, EsINIFormat(generalOptions + i, buffer, sizeof(buffer)), buffer);
 	}
 
-	for (uintptr_t i = 0; i < arrlenu(applications); i++) {
-		if (!applications[i].install) {
-			continue;
-		}
-
-		for (uintptr_t j = 0; j < arrlenu(applications[i].handlers); j++) {
-			Handler *handler = applications[i].handlers + j;
-			int handlerID = applications[i].id;
-
-			for (uintptr_t i = 0; i < arrlenu(applications); i++) {
-				for (uintptr_t j = 0; j < arrlenu(applications[i].fileTypes); j++) {
-					FileType *fileType = applications[i].fileTypes + j;
-
-					if (0 == strcmp(handler->extension, fileType->extension)) {
-						handler->fileTypeID = fileType->id;
-
-						if (0 == strcmp(handler->action, "open")) {
-							fileType->openID = handlerID;
-						} else {
-							Log("Warning: unrecognised handler action '%s'.\n", handler->action);
-						}
-					}
-				}
-			}
-
-			if (!handler->fileTypeID) {
-				Log("Warning: could not find a file_type entry for handler with extension '%s' in application '%s'.\n",
-						handler->extension, applications[i].name);
-			}
-		}
-	}
-
 	for (uintptr_t i = 0; i < arrlenu(applications); i++) {
 		if (!applications[i].install) {
 			continue;
@@ -931,21 +949,13 @@ void OutputSystemConfiguration() {
 			FilePrintFormat(file, "%s=%s\n", applications[i].properties[j].key, applications[i].properties[j].value);
 		}
 
-		for (uintptr_t j = 0; j < arrlenu(applications[i].fileTypes); j++) {
-			FilePrintFormat(file, "\n[file_type]\n");
-			FilePrintFormat(file, "id=%d\n", applications[i].fileTypes[j].id);
-			FilePrintFormat(file, "extension=%s\n", applications[i].fileTypes[j].extension);
-			FilePrintFormat(file, "name=%s\n", applications[i].fileTypes[j].name);
-			FilePrintFormat(file, "icon=%s\n", applications[i].fileTypes[j].icon);
-			FilePrintFormat(file, "open=%d\n", applications[i].fileTypes[j].openID);
-			FilePrintFormat(file, "has_thumbnail_generator=%d\n", applications[i].fileTypes[j].hasThumbnailGenerator);
-		}
+		for (uintptr_t j = 0; j < arrlenu(applications[i].fileTypeLines); j++) {
+			char buffer[4096];
+			FileWrite(file, EsINIFormat(applications[i].fileTypeLines + j, buffer, sizeof(buffer)), buffer);
 
-		for (uintptr_t j = 0; j < arrlenu(applications[i].handlers); j++) {
-			FilePrintFormat(file, "\n[handler]\n");
-			FilePrintFormat(file, "action=%s\n", applications[i].handlers[j].action);
-			FilePrintFormat(file, "application=%d\n", applications[i].id);
-			FilePrintFormat(file, "file_type=%d\n", applications[i].handlers[j].fileTypeID);
+			if (!applications[i].fileTypeLines[j].keyBytes) {
+				FilePrintFormat(file, "application=%d\n", applications[i].id);
+			}
 		}
 	}
 
@@ -1752,8 +1762,7 @@ int main(int argc, char **argv) {
 		arrfree(applications[i].sources);
 		arrfree(applications[i].dependencyFiles);
 		arrfree(applications[i].bundleInputFiles);
-		arrfree(applications[i].fileTypes);
-		arrfree(applications[i].handlers);
+		arrfree(applications[i].fileTypeLines);
 	}
 
 	arrfree(applicationManifests);
diff --git a/util/build_core.ini b/util/build_core.ini
index 232b032..8b020a8 100644
--- a/util/build_core.ini
+++ b/util/build_core.ini
@@ -9,10 +9,9 @@ permission_run_temporary_application=1
 source=util/build_core.c
 
 [file_type]
-extension=build_core
+match=ext:build_core
 name=Build config
 icon=icon_text_x_makefile
-
-[handler]
-extension=build_core
-action=open
+uuid=6F-2A-23-16-AF-A3-D0-FB-95-06-52-B3-67-FB-37-FA
+actions=open
+textual=1
diff --git a/util/designer2.cpp b/util/designer2.cpp
index a8dcfe8..94a98ec 100644
--- a/util/designer2.cpp
+++ b/util/designer2.cpp
@@ -3758,6 +3758,9 @@ int _UIInstanceCallback(EsInstance *instance, EsMessage *message) {
 	if (message->type == ES_MSG_INSTANCE_SAVE) {
 		fileStore = message->instanceSave.file;
 		DocumentSave(nullptr);
+		EsUniqueIdentifier type = (EsUniqueIdentifier) 
+			{{ 0x26, 0x4A, 0xE0, 0x6C, 0x0F, 0xE8, 0x2C, 0xE7, 0xF4, 0x6E, 0x4E, 0x76, 0x5B, 0x4A, 0xCF, 0x4F }};
+		EsFileStoreSetContentType(fileStore, type);
 		EsInstanceSaveComplete(instance, fileStore, true);
 		fileStore = nullptr;
 	} else if (message->type == ES_MSG_INSTANCE_OPEN) {
diff --git a/util/designer2.ini b/util/designer2.ini
index 95c21df..810a43a 100644
--- a/util/designer2.ini
+++ b/util/designer2.ini
@@ -7,10 +7,8 @@ source=util/designer2.cpp
 compile_flags=-D UI_ESSENCE -Wno-unused-parameter
 
 [file_type]
-extension=designer
+match=ext:designer
 name=Designer file
 icon=icon_text_css
-
-[handler]
-extension=designer
-action=open
+uuid=26-4A-E0-6C-0F-E8-2C-E7-F4-6E-4E-76-5B-4A-CF-4F
+actions=open