wip long-form spec stuff

SPEC.md

@@ -3,6 +3,90 @@
 This is the kinda-formal specification for KDL, including the intended data
 model and the grammar.
 
+## Introduction
+
+KDL is a node-oriented document language. Its niche and purpose overlaps with
+XML, and as do many of its semantics. You can use KDL both as a configuration
+language, and a data exchange or storage format, if you so choose.
+
+## Components
+
+### Document
+
+The toplevel concept of KDL is a Document. A Document is composed of one or more
+[Nodes](#node), separated by newlines and whitespace, and eventually terminated by an EOF.
+
+#### Example
+
+The following is a document composed of two toplevel nodes:
+
+```kdl
+foo {
+    bar
+}
+baz
+```
+
+### Node
+
+Being a node-oriented language means that the real core component of any KDL
+document is the "node". Every node must have a name, which is either a legal
+[Identifier](#identifier), or a quoted [String](#string).
+
+Following the name are one or more [Whitespace](#whitespace) components,
+followed by zero or more whitespace-separated [Values](#value) or
+[Properties](#property). Finally, a node is terminated by either a
+[Newline](#newline), a [Children Block](#children-block), a semicolon (`;`) or
+the end of the
+file/stream (an `EOF`).
+
+When present in the list of Properties and Values, plain Values (those not
+attached to a Property), each "anonymous" value should be treated as a
+Property whose key is its current index among _anonymous values_ in the same
+node, starting from 0, as a string. Named properties do not count towarrds
+this index.
+
+That is, the following two nodes are semantically equivalent:
+
+```kdl
+foo 1 key="val" 2
+foo "0"=1 "1"=2 key="val"
+```
+
+#### Example
+
+```kdl
+foo 1 key="val" 3 {
+    bar
+    baz
+}
+```
+
+### Identifier
+
+A bare Identifier is composed of any unicode codepoint other than [non-initial
+characters](#non-inidital-characters), followed by any number of unicode
+codepoints other than [non-identifier characters](#non-identifier-characters).
+Identifiers are terminated by [Whitespace](#whitespace) or
+[Newlines](#newline).
+
+### Non-initial characters
+
+The following characters cannot be the first character in a bare
+[Identifier](#identifier):
+
+* Any of "/\\{};[]=,"
+* Any decimal digit (0-9)
+* Any [non-identifier characters](#non-identifier-characters)
+
+### Non-identifier characters
+
+The following characters cannot be used anywhere in a bare [Identifier](#identifier):
+
+* Any codepoint with hexadecimal value `0x20` or below.
+* Any codepoint with hexadecimal value higher than `0x10FFF`.
+* Any of "\\{};[]=,"
+
 ## Full Grammar
 
 ```