mirror of https://github.com/kdl-org/kdl.git
1247 lines
42 KiB
Plaintext
1247 lines
42 KiB
Plaintext
|
|
|
|
|
|
|
|
KDL Community K. Marchán
|
|
Microsoft
|
|
KDL Contributors
|
|
18 February 2025
|
|
|
|
|
|
The KDL Document Language
|
|
draft-marchan-kdl2-latest
|
|
|
|
Abstract
|
|
|
|
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.
|
|
|
|
This is the formal specification for KDL, including the intended data
|
|
model and the grammar.
|
|
|
|
This document describes an unreleased minor change to KDL. For the
|
|
latest oficial version of the language, see https://kdl.dev/spec.
|
|
|
|
About This Document
|
|
|
|
This note is to be removed before publishing as an RFC.
|
|
|
|
Status information for this document may be found at
|
|
https://datatracker.ietf.org/doc/draft-marchan-kdl2/.
|
|
|
|
information can be found at https://kdl.dev/.
|
|
|
|
Source for this draft and an issue tracker can be found at
|
|
https://github.com/kdl-org/kdl.
|
|
|
|
License
|
|
|
|
This work is licensed under Creative Commons Attribution-ShareAlike
|
|
4.0 International. To view a copy of this license, visit
|
|
https://creativecommons.org/licenses/by-sa/4.0/
|
|
|
|
Table of Contents
|
|
|
|
1. Compatibility
|
|
2. Introduction
|
|
3. Components
|
|
3.1. Document
|
|
3.1.1. Example
|
|
3.2. Node
|
|
3.2.1. Example
|
|
3.3. Line Continuation
|
|
3.3.1. Example
|
|
3.4. Property
|
|
3.5. Argument
|
|
3.5.1. Example
|
|
3.6. Children Block
|
|
3.6.1. Example
|
|
3.7. Value
|
|
3.8. Type Annotation
|
|
3.8.1. Reserved Type Annotations for Numbers Without Decimals:
|
|
3.8.2. Reserved Type Annotations for Numbers With Decimals:
|
|
3.8.3. Reserved Type Annotations for Strings:
|
|
3.8.4. Examples
|
|
3.9. String
|
|
3.10. Identifier String
|
|
3.10.1. Non-initial characters
|
|
3.10.2. Non-identifier characters
|
|
3.11. Quoted String
|
|
3.11.1. Escapes
|
|
3.12. Multi-line String
|
|
3.12.1. Newline Normalization
|
|
3.12.2. Examples
|
|
3.12.3. Interaction with Whitespace Escapes
|
|
3.13. Raw String
|
|
3.13.1. Example
|
|
3.14. Number
|
|
3.14.1. Keyword Numbers
|
|
3.15. Boolean
|
|
3.15.1. Example
|
|
3.16. Null
|
|
3.16.1. Example
|
|
3.17. Whitespace
|
|
3.17.1. Single-line comments
|
|
3.17.2. Multi-line comments
|
|
3.17.3. Slashdash comments
|
|
3.18. Newline
|
|
3.19. Disallowed Literal Code Points
|
|
4. Full Grammar
|
|
4.1. Grammar language
|
|
Authors' Addresses
|
|
|
|
1. Compatibility
|
|
|
|
KDL 2.0 is designed such that for any given KDL document written as
|
|
KDL 1.0 (./SPEC_v1.md) or KDL 2.0, the parse will either fail
|
|
completely, or, if the parse succeeds, the data represented by a v1
|
|
or v2 parser will be identical. This means that it's safe to use a
|
|
fallback parsing strategy in order to support both v1 and v2
|
|
simultaneously. For example, node "foo" is a valid node in both
|
|
versions, and should be represented identically by parsers.
|
|
|
|
A version marker /- kdl-version 2 (or 1) _MAY_ be added to the
|
|
beginning of a KDL document, optionally preceded by the BOM, and
|
|
parsers _MAY_ use that as a hint as to which version to parse the
|
|
document as.
|
|
|
|
2. 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.
|
|
|
|
The bulk of this document is dedicated to a long-form description of
|
|
all Components (Section 3) of a KDL document. There is also a much
|
|
more terse Grammar (Section 4) at the end of the document that covers
|
|
most of the rules, with some semantic exceptions involving the data
|
|
model.
|
|
|
|
KDL is designed to be easy to read _and_ easy to implement.
|
|
|
|
In this document, references to "left" or "right" refer to directions
|
|
in the _data stream_ towards the beginning or end, respectively; in
|
|
other words, the directions if the data stream were only ASCII text.
|
|
They do not refer to the writing direction of text, which can flow in
|
|
either direction, depending on the characters used.
|
|
|
|
3. Components
|
|
|
|
3.1. Document
|
|
|
|
The toplevel concept of KDL is a Document. A Document is composed of
|
|
zero or more Nodes (Section 3.2), separated by newlines, semicolons,
|
|
and whitespace, and eventually terminated by an EOF.
|
|
|
|
All KDL documents MUST be encoded in UTF-8 and conform to the
|
|
specifications in this document.
|
|
|
|
3.1.1. Example
|
|
|
|
The following is a document composed of two toplevel nodes:
|
|
|
|
foo {
|
|
bar
|
|
}
|
|
baz
|
|
|
|
3.2. 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
|
|
must be a String (Section 3.9).
|
|
|
|
The name may be preceded by a Type Annotation (Section 3.8) to
|
|
further clarify its type, particularly in relation to its parent
|
|
node. (For example, clarifying that a particular date child node is
|
|
for the _publication_ date, rather than the last-modified date, with
|
|
(published)date.)
|
|
|
|
Following the name are zero or more Arguments (Section 3.5) or
|
|
Properties (Section 3.4), separated by either whitespace
|
|
(Section 3.17) or a slash-escaped line continuation (Section 3.3).
|
|
Arguments and Properties may be interspersed in any order, much like
|
|
is common with positional arguments vs options in command line tools.
|
|
Collectively, Arguments and Properties may be referred to as
|
|
"Entries".
|
|
|
|
Children (Section 3.6) can be placed after the name and the optional
|
|
Entries, possibly separated by either whitespace or a slash-escaped
|
|
line continuation.
|
|
|
|
Arguments are ordered relative to each other and that order must be
|
|
preserved in order to maintain the semantics. Properties between
|
|
Arguments do not affect Argument ordering.
|
|
|
|
By contrast, Properties _SHOULD NOT_ be assumed to be presented in a
|
|
given order. Children (Section 3.6) should be used if an order-
|
|
sensitive key/value data structure must be represented in KDL. Cf.
|
|
JSON objects preserving key order.
|
|
|
|
Nodes _MAY_ be prefixed with Slashdash (Section 3.17.3) to "comment
|
|
out" the entire node, including its properties, arguments, and
|
|
children, and make it act as plain whitespace, even if it spreads
|
|
across multiple lines.
|
|
|
|
Finally, a node is terminated by either a Newline (Section 3.18), a
|
|
semicolon (;), the end of its parent's child block (}) or the end of
|
|
the file/stream (an EOF).
|
|
|
|
3.2.1. Example
|
|
|
|
// `foo` will have an Argument value list like `[1, 3]`.
|
|
foo 1 key=val 3 {
|
|
bar
|
|
(role)baz 1 2
|
|
}
|
|
|
|
3.3. Line Continuation
|
|
|
|
Line continuations allow Nodes (Section 3.2) to be spread across
|
|
multiple lines.
|
|
|
|
A line continuation is a \ character followed by zero or more
|
|
whitespace items (including multiline comments) and an optional
|
|
single-line comment. It must be terminated by a Newline
|
|
(Section 3.18) (including the Newline that is part of single-line
|
|
comments).
|
|
|
|
Following a line continuation, processing of a Node can continue as
|
|
usual.
|
|
|
|
3.3.1. Example
|
|
|
|
my-node 1 2 \ // comments are ok after \
|
|
3 4 // This is the actual end of the Node.
|
|
|
|
3.4. Property
|
|
|
|
A Property is a key/value pair attached to a Node (Section 3.2). A
|
|
Property is composed of a String (Section 3.9), followed immediately
|
|
by an equals sign (=, U+003D), and then a Value (Section 3.7).
|
|
|
|
Properties should be interpreted left-to-right, with rightmost
|
|
properties with identical names overriding earlier properties. That
|
|
is:
|
|
|
|
node a=1 a=2
|
|
|
|
In this example, the node's a value must be 2, not 1.
|
|
|
|
No other guarantees about order should be expected by implementers.
|
|
Deserialized representations may iterate over properties in any order
|
|
and still be spec-compliant.
|
|
|
|
Properties _MAY_ be prefixed with /- to "comment out" the entire
|
|
token and make it act as plain whitespace, even if it spreads across
|
|
multiple lines.
|
|
|
|
3.5. Argument
|
|
|
|
An Argument is a bare Value (Section 3.7) attached to a Node
|
|
(Section 3.2), with no associated key. It shares the same space as
|
|
Properties (Section 3.4), and may be interleaved with them.
|
|
|
|
A Node may have any number of Arguments, which should be evaluated
|
|
left to right. KDL implementations _MUST_ preserve the order of
|
|
Arguments relative to each other (not counting Properties).
|
|
|
|
Arguments _MAY_ be prefixed with /- to "comment out" the entire token
|
|
and make it act as plain whitespace, even if it spreads across
|
|
multiple lines.
|
|
|
|
3.5.1. Example
|
|
|
|
my-node 1 2 3 a b c
|
|
|
|
3.6. Children Block
|
|
|
|
A children block is a block of Nodes (Section 3.2), surrounded by {
|
|
and }. They are an optional part of nodes, and create a hierarchy of
|
|
KDL nodes.
|
|
|
|
Regular node termination rules apply, which means multiple nodes can
|
|
be included in a single-line children block, as long as they're all
|
|
terminated by ;.
|
|
|
|
3.6.1. Example
|
|
|
|
parent {
|
|
child1
|
|
child2
|
|
}
|
|
|
|
parent { child1; child2 }
|
|
|
|
3.7. Value
|
|
|
|
A value is either: a String (Section 3.9), a Number (Section 3.14), a
|
|
Boolean (Section 3.15), or Null (Section 3.16).
|
|
|
|
Values _MUST_ be either Arguments (Section 3.5) or values of
|
|
Properties (Section 3.4). Only String (Section 3.9) values may be
|
|
used as Node (Section 3.2) names or Property (Section 3.4) keys.
|
|
|
|
Values (both as arguments and in properties) _MAY_ be prefixed by a
|
|
single Type Annotation (Section 3.8).
|
|
|
|
3.8. Type Annotation
|
|
|
|
A type annotation is a prefix to any Node Name (Section 3.2) or Value
|
|
(Section 3.7) that includes a _suggestion_ of what type the value is
|
|
_intended_ to be treated as, or as a _context-specific elaboration_
|
|
of the more generic type the node name indicates.
|
|
|
|
Type annotations are written as a set of ( and ) with a single String
|
|
(Section 3.9) in it. It may contain Whitespace after the ( and
|
|
before the ), and may be separated from its target by Whitespace.
|
|
|
|
KDL does not specify any restrictions on what implementations might
|
|
do with these annotations. They are free to ignore them, or use them
|
|
to make decisions about how to interpret a value.
|
|
|
|
Additionally, the following type annotations MAY be recognized by KDL
|
|
parsers and, if used, SHOULD interpret these types as follows:
|
|
|
|
3.8.1. Reserved Type Annotations for Numbers Without Decimals:
|
|
|
|
Signed integers of various sizes (the number is the bit size):
|
|
|
|
* i8
|
|
|
|
* i16
|
|
|
|
* i32
|
|
|
|
* i64
|
|
|
|
* i128
|
|
|
|
Unsigned integers of various sizes (the number is the bit size):
|
|
|
|
* u8
|
|
|
|
* u16
|
|
|
|
* u32
|
|
|
|
* u64
|
|
|
|
* u128
|
|
|
|
Platform-dependent integer types, both signed and unsigned:
|
|
|
|
* isize
|
|
|
|
* usize
|
|
|
|
3.8.2. Reserved Type Annotations for Numbers With Decimals:
|
|
|
|
IEEE 754 floating point numbers, both single (32) and double (64)
|
|
precision:
|
|
|
|
* f32
|
|
|
|
* f64
|
|
|
|
IEEE 754-2008 decimal floating point numbers
|
|
|
|
* decimal64
|
|
|
|
* decimal128
|
|
|
|
3.8.3. Reserved Type Annotations for Strings:
|
|
|
|
* date-time: ISO8601 date/time format.
|
|
|
|
* time: "Time" section of ISO8601.
|
|
|
|
* date: "Date" section of ISO8601.
|
|
|
|
* duration: ISO8601 duration format.
|
|
|
|
* decimal: IEEE 754-2008 decimal string format.
|
|
|
|
* currency: ISO 4217 currency code.
|
|
|
|
* country-2: ISO 3166-1 alpha-2 country code.
|
|
|
|
* country-3: ISO 3166-1 alpha-3 country code.
|
|
|
|
* country-subdivision: ISO 3166-2 country subdivision code.
|
|
|
|
* email: RFC5322 email address.
|
|
|
|
* idn-email: RFC6531 internationalized email address.
|
|
|
|
* hostname: RFC1123 internet hostname (only ASCII segments)
|
|
|
|
* idn-hostname: RFC5890 internationalized internet hostname (only xn
|
|
---prefixed ASCII "punycode" segments, or non-ASCII segments)
|
|
|
|
* ipv4: RFC2673 dotted-quad IPv4 address.
|
|
|
|
* ipv6: RFC2373 IPv6 address.
|
|
|
|
* url: RFC3986 URI.
|
|
|
|
* url-reference: RFC3986 URI Reference.
|
|
|
|
* irl: RFC3987 Internationalized Resource Identifier.
|
|
|
|
* irl-reference: RFC3987 Internationalized Resource Identifier
|
|
Reference.
|
|
|
|
* url-template: RFC6570 URI Template.
|
|
|
|
* uuid: RFC4122 UUID.
|
|
|
|
* regex: Regular expression. Specific patterns may be
|
|
implementation-dependent.
|
|
|
|
* base64: A Base64-encoded string, denoting arbitrary binary data.
|
|
|
|
* base85: An Ascii85 (https://en.wikipedia.org/wiki/Ascii85)-encoded
|
|
string, denoting arbitrary binary data.
|
|
|
|
3.8.4. Examples
|
|
|
|
node (u8)123
|
|
node prop=(regex).*
|
|
(published)date "1970-01-01"
|
|
(contributor)person name="Foo McBar"
|
|
|
|
3.9. String
|
|
|
|
Strings in KDL represent textual UTF-8 Values (Section 3.7). A
|
|
String is either an Identifier String (Section 3.10) (like foo), a
|
|
Quoted String (Section 3.11) (like "foo") or a Multi-Line String
|
|
(Section 3.12). Both Quoted and Multiline strings come in normal and
|
|
Raw String (Section 3.13) variants (like #"foo"#):
|
|
|
|
* Identifier Strings let you write short, "single-word" strings with
|
|
a minimum of syntax
|
|
|
|
* Quoted Strings let you write strings "like normal", with
|
|
whitespace and escapes.
|
|
|
|
* Multi-Line Strings let you write strings across multiple lines and
|
|
with indentation that's not part of the string value.
|
|
|
|
* Raw Strings don't allow any escapes, allowing you to not worry
|
|
about the string's content containing anything that might look
|
|
like an escape.
|
|
|
|
Strings _MUST_ be represented as UTF-8 values.
|
|
|
|
Strings _MUST NOT_ include the code points for disallowed literal
|
|
code points (Section 3.19) directly. Quoted and Multi-Line Strings
|
|
may include these code points as _values_ by representing them with
|
|
their corresponding \u{...} escape.
|
|
|
|
3.10. Identifier String
|
|
|
|
An Identifier String (sometimes referred to as just an "identifier")
|
|
is composed of any Unicode Scalar Value (https://unicode.org/
|
|
glossary/#unicode_scalar_value) other than non-initial characters
|
|
(Section 3.10.1), followed by any number of Unicode Scalar Values
|
|
other than non-identifier characters (Section 3.10.2).
|
|
|
|
A handful of patterns are disallowed, to avoid confusion with other
|
|
values:
|
|
|
|
* idents that appear to start with a Number (Section 3.14) (like
|
|
1.0v2 or -1em) or the "almost a number" pattern of a decimal point
|
|
without a leading digit (like .1).
|
|
|
|
* idents that are the language keywords (inf, -inf, nan, true,
|
|
false, and null) without their leading #.
|
|
|
|
Identifiers that match these patterns _MUST_ be treated as a syntax
|
|
error; such values can only be written as quoted or raw strings. The
|
|
precise details of the identifier syntax is specified in the Full
|
|
Grammar in Section 4.
|
|
|
|
3.10.1. Non-initial characters
|
|
|
|
The following characters cannot be the first character in an
|
|
Identifier String (Section 3.10):
|
|
|
|
* Any decimal digit (0-9)
|
|
|
|
* Any non-identifier characters (Section 3.10.2)
|
|
|
|
Additionally, the following initial characters impose limitations on
|
|
subsequent characters:
|
|
|
|
* the + and - characters can only be used as an initial character if
|
|
the second character is _not_ a digit. If the second character is
|
|
., then the third character must _not_ be a digit.
|
|
|
|
* the . character can only be used as an initial character if the
|
|
second character is _not_ a digit.
|
|
|
|
This allows identifiers to look like --this or .md, and removes the
|
|
ambiguity of having an identifier look like a number.
|
|
|
|
3.10.2. Non-identifier characters
|
|
|
|
The following characters cannot be used anywhere in a Identifier
|
|
String (Section 3.10):
|
|
|
|
* Any of (){}[]/\"#;=
|
|
|
|
* Any Whitespace (Section 3.17) or Newline (Section 3.18).
|
|
|
|
* Any disallowed literal code points (Section 3.19) in KDL
|
|
documents.
|
|
|
|
3.11. Quoted String
|
|
|
|
A Quoted String is delimited by " on either side of any number of
|
|
literal string characters except unescaped " and \.
|
|
|
|
Literal Newline (Section 3.18) characters can only be included if
|
|
they are Escaped Whitespace (Section 3.11.1.1), which discards them
|
|
from the string value. Actually including a newline in the value
|
|
requires using a newline escape sequence, like \n, or using a Multi-
|
|
Line String (Section 3.12) which is actually designed for strings
|
|
stretching across multiple lines.
|
|
|
|
Like Identifier Strings, Quoted Strings _MUST NOT_ include any of the
|
|
disallowed literal code-points (Section 3.19) as code points in their
|
|
body.
|
|
|
|
Quoted Strings have a Raw String (Section 3.13) variant, which
|
|
disallows escapes.
|
|
|
|
3.11.1. Escapes
|
|
|
|
In addition to literal code points, a number of "escapes" are
|
|
supported in Quoted Strings. "Escapes" are the character \ followed
|
|
by another character, and are interpreted as described in the
|
|
following table:
|
|
|
|
+==============+=========+=========================================+
|
|
| Name | Escape | Code Pt |
|
|
+==============+=========+=========================================+
|
|
| Line Feed | \n | U+000A |
|
|
+--------------+---------+-----------------------------------------+
|
|
| Carriage | \r | U+000D |
|
|
| Return | | |
|
|
+--------------+---------+-----------------------------------------+
|
|
| Character | \t | U+0009 |
|
|
| Tabulation | | |
|
|
| (Tab) | | |
|
|
+--------------+---------+-----------------------------------------+
|
|
| Reverse | \\ | U+005C |
|
|
| Solidus | | |
|
|
| (Backslash) | | |
|
|
+--------------+---------+-----------------------------------------+
|
|
| Quotation | \" | U+0022 |
|
|
| Mark (Double | | |
|
|
| Quote) | | |
|
|
+--------------+---------+-----------------------------------------+
|
|
| Backspace | \b | U+0008 |
|
|
+--------------+---------+-----------------------------------------+
|
|
| Form Feed | \f | U+000C |
|
|
+--------------+---------+-----------------------------------------+
|
|
| Space | \s | U+0020 |
|
|
+--------------+---------+-----------------------------------------+
|
|
| Unicode | \u{(1-6 | Code point described by hex characters, |
|
|
| Escape | hex | as long as it represents a Unicode |
|
|
| | chars)} | Scalar Value (https://unicode.org/ |
|
|
| | | glossary/#unicode_scalar_value) |
|
|
+--------------+---------+-----------------------------------------+
|
|
| Whitespace | See | N/A |
|
|
| Escape | below | |
|
|
+--------------+---------+-----------------------------------------+
|
|
|
|
Table 1
|
|
|
|
3.11.1.1. Escaped Whitespace
|
|
|
|
In addition to escaping individual characters, \ can also escape
|
|
whitespace. When a \ is followed by one or more literal whitespace
|
|
characters, the \ and all of that whitespace are discarded. For
|
|
example,
|
|
|
|
"Hello World"
|
|
|
|
and
|
|
|
|
"Hello \ World"
|
|
|
|
are semantically identical. See whitespace (Section 3.17) and
|
|
newlines (Section 3.18) for how whitespace is defined.
|
|
|
|
Note that only literal whitespace is escaped; whitespace escapes (\n
|
|
and such) are retained. For example, these strings are all
|
|
semantically identical:
|
|
|
|
"Hello\ \nWorld"
|
|
|
|
"Hello\n\
|
|
World"
|
|
|
|
"Hello\nWorld"
|
|
|
|
"""
|
|
Hello
|
|
World
|
|
"""
|
|
|
|
3.11.1.2. Invalid escapes
|
|
|
|
Except as described in the escapes table, above, \ _MUST NOT_ precede
|
|
any other characters in a string.
|
|
|
|
3.12. Multi-line String
|
|
|
|
Multi-Line Strings support multiple lines with literal, non-escaped
|
|
Newlines. They must use a special multi-line syntax, and they
|
|
automatically "dedent" the string, allowing its value to be indented
|
|
to a visually matching level as desired.
|
|
|
|
A Multi-Line String is opened and closed by _three_ double-quote
|
|
characters, like """. Its first line _MUST_ immediately start with a
|
|
Newline (Section 3.18) after its opening """. Its final line _MUST_
|
|
contain only whitespace before the closing """. All in-between lines
|
|
that contain non-newline, non-whitespace characters _MUST_ start with
|
|
_at least_ the exact same whitespace as the final line (precisely
|
|
matching codepoints, not merely counting characters or "size"); they
|
|
may contain additional whitespace following this prefix. The lines
|
|
in between may contain unescaped " (but no unescaped """ as this
|
|
would close the string).
|
|
|
|
The value of the Multi-Line String omits the first and last Newline,
|
|
the Whitespace of the last line, and the matching Whitespace prefix
|
|
on all intermediate lines. The first and last Newline can be the
|
|
same character (that is, empty multi-line strings are legal).
|
|
|
|
In other words, the final line specifies the whitespace prefix that
|
|
will be removed from all other lines.
|
|
|
|
Multi-line Strings that do not immediately start with a Newline and
|
|
whose final """ is not preceeded by optional whitespace and a Newline
|
|
are illegal. This also means that """ may not be used for a single-
|
|
line String (e.g. """foo""").
|
|
|
|
3.12.1. Newline Normalization
|
|
|
|
Literal Newline sequences in Multi-line Strings must be normalized to
|
|
a single U+000A (LF) during deserialization. This means, for
|
|
example, that CR LF becomes a single LF during parsing.
|
|
|
|
This normalization does not apply to non-literal Newlines entered
|
|
using escape sequences. That is:
|
|
|
|
multi-line """
|
|
\r\n[CRLF]
|
|
foo[CRLF]
|
|
"""
|
|
|
|
becomes:
|
|
|
|
single-line "\r\n\nfoo"
|
|
|
|
For clarity: this normalization applies to each individual Newline
|
|
sequence. That is, the literal sequence CRLF CRLF becomes LF LF, not
|
|
LF.
|
|
|
|
3.12.2. Examples
|
|
|
|
3.12.2.1. Indented multi-line string
|
|
|
|
multi-line """
|
|
foo
|
|
This is the base indentation
|
|
bar
|
|
"""
|
|
|
|
This example's string value will be:
|
|
|
|
foo
|
|
This is the base indentation
|
|
bar
|
|
|
|
which is equivalent to
|
|
|
|
" foo\nThis is the base indentation\n bar"
|
|
|
|
when written as a single-line string.
|
|
|
|
3.12.2.2. Shorter last-line indent
|
|
|
|
If the last line wasn't indented as far, it won't dedent the rest of
|
|
the lines as much:
|
|
|
|
multi-line """
|
|
foo
|
|
This is no longer on the left edge
|
|
bar
|
|
"""
|
|
|
|
This example's string value will be:
|
|
|
|
foo
|
|
This is no longer on the left edge
|
|
bar
|
|
|
|
Equivalent to
|
|
|
|
" foo\n This is no longer on the left edge\n bar"
|
|
|
|
3.12.2.3. Empty lines
|
|
|
|
Empty lines can contain any whitespace, or none at all, and will be
|
|
reflected as empty in the value:
|
|
|
|
multi-line """
|
|
Indented a bit
|
|
|
|
A second indented paragraph.
|
|
"""
|
|
|
|
This example's string value will be:
|
|
|
|
Indented a bit.
|
|
|
|
A second indented paragraph.
|
|
|
|
Equivalent to
|
|
|
|
"Indented a bit.\n\nA second indented paragraph."
|
|
|
|
3.12.2.4. Syntax errors
|
|
|
|
The following yield *syntax errors*:
|
|
|
|
multi-line """can't be single line"""
|
|
|
|
multi-line """
|
|
closing quote with non-whitespace prefix"""
|
|
|
|
multi-line """stuff
|
|
"""
|
|
|
|
// Every line must share the exact same prefix as the closing line.
|
|
multi-line """[\n]
|
|
[tab]a[\n]
|
|
[space][space]b[\n]
|
|
[space][tab][\n]
|
|
[tab]"""
|
|
|
|
3.12.3. Interaction with Whitespace Escapes
|
|
|
|
Multi-line strings support the same mechanism for escaping whitespace
|
|
as Quoted Strings.
|
|
|
|
When processing a Multi-line String, implementations MUST dedent the
|
|
string _after_ resolving all whitespace escapes, but _before_
|
|
resolving other backslash escapes. This means a whitespace escape
|
|
that attempts to escape the final line's newline and/or whitespace
|
|
prefix can be invalid: if removing escaped whitespace places the
|
|
closing """ on a line with non-whitespace characters, this escape is
|
|
invalid.
|
|
|
|
For example, the following example is illegal:
|
|
|
|
"""
|
|
foo
|
|
bar\
|
|
"""
|
|
|
|
// equivalent to
|
|
"""
|
|
foo
|
|
bar"""
|
|
|
|
while the following example is allowed
|
|
|
|
"""
|
|
foo \
|
|
bar
|
|
baz
|
|
\ """
|
|
|
|
// equivalent to
|
|
"""
|
|
foo bar
|
|
baz
|
|
"""
|
|
|
|
3.13. Raw String
|
|
|
|
Both Quoted (Section 3.11) and Multi-Line Strings (Section 3.12) have
|
|
Raw String variants, which are identical in syntax except they do not
|
|
support \-escapes. This includes line-continuation escapes (\ + ws
|
|
collapsing to nothing). They otherwise share the same properties as
|
|
far as literal Newline (Section 3.18) characters go, multi-line
|
|
rules, and the requirement of UTF-8 representation.
|
|
|
|
The Raw String variants are indicated by preceding the strings's
|
|
opening quotes with one or more # characters. The string is then
|
|
closed by its normal closing quotes, followed by a _matching_ number
|
|
of # characters. This means that the string may contain any
|
|
combination of " and # characters other than its closing delimiter
|
|
(e.g., if a raw string starts with ##", it can contain " or "#, but
|
|
not "## or "###).
|
|
|
|
Like other Strings, Raw Strings _MUST NOT_ include any of the
|
|
disallowed literal code-points (Section 3.19) as code points in their
|
|
body. Unlike with Quoted Strings, these cannot simply be escaped,
|
|
and are thus unrepresentable when using Raw Strings.
|
|
|
|
3.13.1. Example
|
|
|
|
just-escapes #"\n will be literal"#
|
|
|
|
The string contains the literal characters \n will be literal.
|
|
|
|
quotes-and-escapes ##"hello\n\r\asd"#world"##
|
|
|
|
The string contains the literal characters hello\n\r\asd"#world
|
|
|
|
raw-multi-line #"""
|
|
Here's a """
|
|
multiline string
|
|
"""
|
|
without escapes.
|
|
"""#
|
|
|
|
The string contains the value
|
|
|
|
Here's a """
|
|
multiline string
|
|
"""
|
|
without escapes.
|
|
|
|
or equivalently,
|
|
|
|
"Here's a \"\"\"\n multiline string\n \"\"\"\nwithout escapes."
|
|
|
|
as a Quoted String.
|
|
|
|
3.14. Number
|
|
|
|
Numbers in KDL represent numerical Values (Section 3.7). There is no
|
|
logical distinction in KDL between real numbers, integers, and
|
|
floating point numbers. It's up to individual implementations to
|
|
determine how to represent KDL numbers.
|
|
|
|
There are five syntaxes for Numbers: Keywords, Decimal, Hexadecimal,
|
|
Octal, and Binary.
|
|
|
|
* All non-Keyword (Section 3.14.1) numbers may optionally start with
|
|
one of - or +, which determine whether they'll be positive or
|
|
negative.
|
|
|
|
* Binary numbers start with 0b and only allow 0 and 1 as digits,
|
|
which may be separated by _. They represent numbers in radix 2.
|
|
|
|
* Octal numbers start with 0o and only allow digits between 0 and 7,
|
|
which may be separated by _. They represent numbers in radix 8.
|
|
|
|
* Hexadecimal numbers start with 0x and allow digits between 0 and
|
|
9, as well as letters A through F, in either lower or upper case,
|
|
which may be separated by _. They represent numbers in radix 16.
|
|
|
|
* Decimal numbers are a bit more special:
|
|
|
|
- They have no radix prefix.
|
|
|
|
- They use digits 0 through 9, which may be separated by _.
|
|
|
|
- They may optionally include a decimal separator ., followed by
|
|
more digits, which may again be separated by _.
|
|
|
|
- They may optionally be followed by E or e, an optional - or +,
|
|
and more digits, to represent an exponent value.
|
|
|
|
Note that, similar to JSON and some other languages, numbers without
|
|
an integer digit (such as .1) are illegal. They must be written with
|
|
at least one integer digit, like 0.1. (These patterns are also
|
|
disallowed from Identifier Strings (Section 3.10), to avoid
|
|
confusion.)
|
|
|
|
3.14.1. Keyword Numbers
|
|
|
|
There are three special "keyword" numbers included in KDL to
|
|
accomodate the widespread use of IEEE 754
|
|
(https://en.wikipedia.org/wiki/IEEE_754) floats:
|
|
|
|
* #inf - floating point positive infinity.
|
|
|
|
* #-inf - floating point negative infinity.
|
|
|
|
* #nan - floating point NaN/Not a Number.
|
|
|
|
To go along with this and prevent foot guns, the bare Identifier
|
|
Strings (Section 3.10) inf, -inf, and nan are considered illegal
|
|
identifiers and should yield a syntax error.
|
|
|
|
The existence of these keywords does not imply that any numbers be
|
|
represented as IEEE 754 floats. These are simply for clarity and
|
|
convenience for any implementation that chooses to represent their
|
|
numbers in this way.
|
|
|
|
3.15. Boolean
|
|
|
|
A boolean Value (Section 3.7) is either the symbol #true or #false.
|
|
These _SHOULD_ be represented by implementation as boolean logical
|
|
values, or some approximation thereof.
|
|
|
|
3.15.1. Example
|
|
|
|
my-node #true value=#false
|
|
|
|
3.16. Null
|
|
|
|
The symbol #null represents a null Value (Section 3.7). It's up to
|
|
the implementation to decide how to represent this, but it generally
|
|
signals the "absence" of a value.
|
|
|
|
3.16.1. Example
|
|
|
|
my-node #null key=#null
|
|
|
|
3.17. Whitespace
|
|
|
|
The following characters should be treated as non-Newline
|
|
(Section 3.18) white space
|
|
(https://www.unicode.org/Public/UCD/latest/ucd/PropList.txt):
|
|
|
|
+===========================+=========+
|
|
| Name | Code Pt |
|
|
+===========================+=========+
|
|
| Character Tabulation | U+0009 |
|
|
+---------------------------+---------+
|
|
| Space | U+0020 |
|
|
+---------------------------+---------+
|
|
| No-Break Space | U+00A0 |
|
|
+---------------------------+---------+
|
|
| Ogham Space Mark | U+1680 |
|
|
+---------------------------+---------+
|
|
| En Quad | U+2000 |
|
|
+---------------------------+---------+
|
|
| Em Quad | U+2001 |
|
|
+---------------------------+---------+
|
|
| En Space | U+2002 |
|
|
+---------------------------+---------+
|
|
| Em Space | U+2003 |
|
|
+---------------------------+---------+
|
|
| Three-Per-Em Space | U+2004 |
|
|
+---------------------------+---------+
|
|
| Four-Per-Em Space | U+2005 |
|
|
+---------------------------+---------+
|
|
| Six-Per-Em Space | U+2006 |
|
|
+---------------------------+---------+
|
|
| Figure Space | U+2007 |
|
|
+---------------------------+---------+
|
|
| Punctuation Space | U+2008 |
|
|
+---------------------------+---------+
|
|
| Thin Space | U+2009 |
|
|
+---------------------------+---------+
|
|
| Hair Space | U+200A |
|
|
+---------------------------+---------+
|
|
| Narrow No-Break Space | U+202F |
|
|
+---------------------------+---------+
|
|
| Medium Mathematical Space | U+205F |
|
|
+---------------------------+---------+
|
|
| Ideographic Space | U+3000 |
|
|
+---------------------------+---------+
|
|
|
|
Table 2
|
|
|
|
3.17.1. Single-line comments
|
|
|
|
Any text after //, until the next literal Newline (Section 3.18) is
|
|
"commented out", and is considered to be Whitespace (Section 3.17).
|
|
|
|
3.17.2. Multi-line comments
|
|
|
|
In addition to single-line comments using //, comments can also be
|
|
started with /* and ended with */. These comments can span multiple
|
|
lines. They are allowed in all positions where Whitespace
|
|
(Section 3.17) is allowed and can be nested.
|
|
|
|
3.17.3. Slashdash comments
|
|
|
|
Finally, a special kind of comment called a "slashdash", denoted by
|
|
/-, can be used to comment out entire _components_ of a KDL document
|
|
logically, and have those elements not be included as part of the
|
|
parsed document data.
|
|
|
|
Slashdash comments can be used before the following, including before
|
|
their type annotations, if present:
|
|
|
|
* A Node (Section 3.2): the entire Node is treated as Whitespace,
|
|
including all props, args, and children.
|
|
|
|
* An Argument (Section 3.5): the Argument value is treated as
|
|
Whitespace.
|
|
|
|
* A Property (Section 3.4) key: the entire property, including both
|
|
key and value, is treated as Whitespace. A slashdash of just the
|
|
property value is not allowed.
|
|
|
|
* A Children Block (Section 3.6): the entire block, including all
|
|
children within, is treated as Whitespace. Only other children
|
|
blocks, whether slashdashed or not, may follow a slashdashed
|
|
children block.
|
|
|
|
A slashdash may be be followed by any amount of whitespace, including
|
|
newlines and comments (other than other slashdashes), before the
|
|
element that it comments out.
|
|
|
|
3.18. Newline
|
|
|
|
The following character sequences should be treated as new lines
|
|
(https://www.unicode.org/versions/Unicode16.0.0/core-spec/chapter-
|
|
5/#G41643):
|
|
|
|
+=========+===============================+=================+
|
|
| Acronym | Name | Code Pt |
|
|
+=========+===============================+=================+
|
|
| CRLF | Carriage Return and Line Feed | U+000D + U+000A |
|
|
+---------+-------------------------------+-----------------+
|
|
| CR | Carriage Return | U+000D |
|
|
+---------+-------------------------------+-----------------+
|
|
| LF | Line Feed | U+000A |
|
|
+---------+-------------------------------+-----------------+
|
|
| NEL | Next Line | U+0085 |
|
|
+---------+-------------------------------+-----------------+
|
|
| VT | Vertical tab | U+000B |
|
|
+---------+-------------------------------+-----------------+
|
|
| FF | Form Feed | U+000C |
|
|
+---------+-------------------------------+-----------------+
|
|
| LS | Line Separator | U+2028 |
|
|
+---------+-------------------------------+-----------------+
|
|
| PS | Paragraph Separator | U+2029 |
|
|
+---------+-------------------------------+-----------------+
|
|
|
|
Table 3
|
|
|
|
Note that for the purpose of new lines, the specific sequence CRLF is
|
|
considered _a single newline_.
|
|
|
|
3.19. Disallowed Literal Code Points
|
|
|
|
The following code points may not appear literally anywhere in the
|
|
document. They may be represented in Strings (but not Raw Strings)
|
|
using Unicode Escapes (Section 3.11.1) (\u{...}, except for non
|
|
Unicode Scalar Value, which can't be represented even as escapes).
|
|
|
|
* The codepoints U+0000-0008 or the codepoints U+000E-001F (various
|
|
control characters).
|
|
|
|
* U+007F (the Delete control character).
|
|
|
|
* Any codepoint that is not a Unicode Scalar Value
|
|
(https://unicode.org/glossary/#unicode_scalar_value)
|
|
(U+D800-DFFF).
|
|
|
|
* U+200E-200F, U+202A-202E, and U+2066-2069, the unicode "direction
|
|
control" characters (https://www.w3.org/International/questions/
|
|
qa-bidi-unicode-controls)
|
|
|
|
* U+FEFF, aka Zero-width Non-breaking Space (ZWNBSP)/Byte Order Mark
|
|
(BOM), except as the first code point in a document.
|
|
|
|
4. Full Grammar
|
|
|
|
This is the full official grammar for KDL and should be considered
|
|
authoritative if something seems to disagree with the text above.
|
|
The grammar language syntax is defined in Section 4.1.
|
|
|
|
document := bom? version? nodes
|
|
|
|
// Nodes
|
|
nodes := (line-space* node)* line-space*
|
|
|
|
base-node := slashdash? type? node-space* string
|
|
(node-space* (node-space | slashdash) node-prop-or-arg)*
|
|
// slashdashed node-children must always be after props and args.
|
|
(node-space* slashdash node-children)*
|
|
(node-space* node-children)?
|
|
(node-space* slashdash node-children)*
|
|
node-space*
|
|
node := base-node node-terminator
|
|
final-node := base-node node-terminator?
|
|
|
|
// Entries
|
|
node-prop-or-arg := prop | value
|
|
node-children := '{' nodes final-node? '}'
|
|
node-terminator := single-line-comment | newline | ';' | eof
|
|
|
|
prop := string node-space* '=' node-space* value
|
|
value := type? node-space* (string | number | keyword)
|
|
type := '(' node-space* string node-space* ')'
|
|
|
|
// Strings
|
|
string := identifier-string | quoted-string | raw-string ¶
|
|
|
|
identifier-string := unambiguous-ident | signed-ident | dotted-ident
|
|
unambiguous-ident :=
|
|
((identifier-char - digit - sign - '.') identifier-char*)
|
|
- disallowed-keyword-strings
|
|
signed-ident :=
|
|
sign ((identifier-char - digit - '.') identifier-char*)?
|
|
dotted-ident :=
|
|
sign? '.' ((identifier-char - digit) identifier-char*)?
|
|
identifier-char :=
|
|
unicode - unicode-space - newline - [\\/(){};\[\]"#=]
|
|
- disallowed-literal-code-points
|
|
disallowed-keyword-identifiers :=
|
|
'true' | 'false' | 'null' | 'inf' | '-inf' | 'nan'
|
|
|
|
quoted-string :=
|
|
'"' single-line-string-body '"' |
|
|
'"""' newline
|
|
(multi-line-string-body newline)?
|
|
(unicode-space | ws-escape)* '"""'
|
|
single-line-string-body := (string-character - newline)*
|
|
multi-line-string-body := (('"' | '""')? string-character)*
|
|
string-character :=
|
|
'\\' (["\\bfnrts] |
|
|
'u{' hex-unicode '}') |
|
|
ws-escape |
|
|
[^\\"] - disallowed-literal-code-points
|
|
ws-escape := '\\' (unicode-space | newline)+
|
|
hex-digit := [0-9a-fA-F]
|
|
hex-unicode := hex-digit{1, 6} - surrogate - above-max-scalar
|
|
surrogate := [0]{0, 2} [dD] [8-9a-fA-F] hex-digit{2}
|
|
// U+D800-DFFF: D 8 00
|
|
// D F FF
|
|
above-max-scalar = [2-9a-fA-F] hex-digit{5} |
|
|
[1] [1-9a-fA-F] hex-digit{4}
|
|
|
|
|
|
raw-string := '#' raw-string-quotes '#' | '#' raw-string '#'
|
|
raw-string-quotes :=
|
|
'"' single-line-raw-string-body '"' |
|
|
'"""' newline
|
|
(multi-line-raw-string-body newline)?
|
|
unicode-space* '"""'
|
|
single-line-raw-string-body :=
|
|
'' |
|
|
(single-line-raw-string-char - '"')
|
|
single-line-raw-string-char*? |
|
|
'"' (single-line-raw-string-char - '"')
|
|
single-line-raw-string-char*?
|
|
single-line-raw-string-char :=
|
|
unicode - newline - disallowed-literal-code-points
|
|
multi-line-raw-string-body :=
|
|
(unicode - disallowed-literal-code-points)*?
|
|
|
|
// Numbers
|
|
number := keyword-number | hex | octal | binary | decimal
|
|
|
|
decimal := sign? integer ('.' integer)? exponent?
|
|
exponent := ('e' | 'E') sign? integer
|
|
integer := digit (digit | '_')*
|
|
digit := [0-9]
|
|
sign := '+' | '-'
|
|
|
|
hex := sign? '0x' hex-digit (hex-digit | '_')*
|
|
octal := sign? '0o' [0-7] [0-7_]*
|
|
binary := sign? '0b' ('0' | '1') ('0' | '1' | '_')*
|
|
|
|
// Keywords and booleans.
|
|
keyword := boolean | '#null'
|
|
keyword-number := '#inf' | '#-inf' | '#nan'
|
|
boolean := '#true' | '#false'
|
|
|
|
// Specific code points
|
|
bom := '\u{FEFF}'
|
|
disallowed-literal-code-points :=
|
|
See Table (Disallowed Literal Code Points)
|
|
unicode := Any Unicode Scalar Value
|
|
unicode-space := See Table
|
|
(All White_Space unicode characters which are not `newline`)
|
|
|
|
// Comments
|
|
single-line-comment := '//' ^newline* (newline | eof)
|
|
multi-line-comment := '/*' commented-block
|
|
commented-block :=
|
|
'*/' | (multi-line-comment | '*' | '/' | [^*/]+) commented-block
|
|
slashdash := '/-' line-space*
|
|
|
|
// Whitespace
|
|
ws := unicode-space | multi-line-comment
|
|
escline := '\\' ws* (single-line-comment | newline | eof)
|
|
newline := See Table (All Newline White_Space)
|
|
// Whitespace where newlines are allowed.
|
|
line-space := node-space | newline | single-line-comment
|
|
// Whitespace within nodes,
|
|
// where newline-ish things must be esclined.
|
|
node-space := ws* escline ws* | ws+
|
|
|
|
// Version marker
|
|
version :=
|
|
'/-' unicode-space* 'kdl-version' unicode-space+ ('1' | '2')
|
|
unicode-space* newline
|
|
|
|
4.1. Grammar language
|
|
|
|
The grammar language syntax is a combination of ABNF with some regex
|
|
spice thrown in. Specifically:
|
|
|
|
* Single quotes (') are used to denote literal text. \ within a
|
|
literal string is used for escaping other single-quotes, for
|
|
initiating unicode characters using hex values (\u{FEFF}), and for
|
|
escaping \ itself (\\).
|
|
|
|
* * is used for "zero or more", + is used for "one or more", and ?
|
|
is used for "zero or one". Per standard regex semantics, * and +
|
|
are _greedy_; they match as many instances as possible without
|
|
failing the match.
|
|
|
|
* *? (used only in raw strings) indicates a _non-greedy_ match; it
|
|
matches as _few_ instances as possible without failing the match.
|
|
|
|
* ¶ is a _cut point_. It always matches and consumes no characters,
|
|
but once matched, the parser is not allowed to backtrack past that
|
|
point in the source. If a parser would rewind past the cut point,
|
|
it must instead fail the overall parse, as if it had run out of
|
|
options. (This is only used with the raw-string production, to
|
|
ensure the first instance of the appropriate closing quote
|
|
sequence is guaranteed to be the end of the raw string, rather
|
|
than allowing it to potentially consume more of the document
|
|
unexpectedly.)
|
|
|
|
* () can be used to group matches that must be matched together.
|
|
|
|
* a | b means a or b, whichever matches first. If multiple items
|
|
are before a |, they are a single group. a b c | d is equivalent
|
|
to (a b c) | d.
|
|
|
|
* [] are used for regex-style character matches, where any character
|
|
between the brackets will be a single match. \ is used to escape
|
|
\, [, and ]. They also support character ranges (0-9), and
|
|
negation (^)
|
|
|
|
* - is used for "except for" or "minus" whatever follows it. For
|
|
example, a - 'x' means "any a, except something that matches the
|
|
literal 'x'".
|
|
|
|
* The prefix ^ means "something that does not match" whatever
|
|
follows it. For example, ^foo means "must not match foo".
|
|
|
|
* A single definition may be split over multiple lines. Newlines
|
|
are treated as spaces.
|
|
|
|
* // followed by text on its own line is used as comment syntax.
|
|
|
|
Authors' Addresses
|
|
|
|
Katerina Zoé Marchán Salvá
|
|
Microsoft
|
|
|
|
|
|
The KDL Contributors
|