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CLDR-16836 kbd: add EBNF to spec for transforms (#4261)
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- includes ABNF sources, which can be converted TO EBNF with https://www.bottlecaps.de/ebnf-convert/
- includes shell script / workflow test via node-abnf
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srl295 authored Jan 9, 2025
1 parent 5137c81 commit 2b78422
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2 changes: 2 additions & 0 deletions .github/workflows/keyboard.yml
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Expand Up @@ -37,5 +37,7 @@ jobs:
run: npm install -g @keymanapp/kmc
- name: Compile Keyboards
run: kmc --error-reporting build keyboards/3.0/*.xml
- name: Check ABNF
run: bash tools/scripts/keyboard-abnf-tests/check-keyboard-abnf.sh
- name: Run Kbd Charts
run: 'cd docs/charts/keyboards && npm ci && npm run build'
280 changes: 279 additions & 1 deletion docs/ldml/tr35-keyboards.md
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Expand Up @@ -121,6 +121,10 @@ The LDML specification is divided into the following parts:
* [Additional Features](#additional-features)
* [Disallowed Regex Features](#disallowed-regex-features)
* [Replacement syntax](#replacement-syntax)
* [Transform Grammar](#transform-grammar)
* [Transform From Grammar](#transform-from-grammar)
* [Transform To Grammar](#transform-to-grammar)
* [ABNF](#abnf)
* [Element: reorder](#element-reorder)
* [Using `<import>` with `<reorder>` elements](#using-import-with-reorder-elements)
* [Example Post-reorder transforms](#example-post-reorder-transforms)
Expand Down Expand Up @@ -2412,6 +2416,280 @@ Used in the `to=`

Emits the named mark. Also see [Markers](#markers).

#### Transform Grammar

##### Transform From Grammar

The `from=` attribute MUST match the `from-match` rule in this grammar. Not all strings which match this grammar are valid, specifically

The following is the [LDML EBNF](./tr35.md#ebnf) format for the grammar:


```ebnf
[ wfc: No more than 9 capture groups may be present. ]
[ vc: all variables referenced must be defined in the <variables> element ]

from-match
::= '^'? atoms
atoms ::= atom ( '|'? atom )*
atom ::= quark quantifier?
quark ::= non-group
| group
non-group
::= simple-matcher
| escaped-codepoints
| variable
variable ::= string-variable
| set-variable
string-variable
::= '${' var-id '}'
set-variable
::= '$[' var-id ']'
var-id ::= IDCHAR+
group ::= capturing-group
| non-capturing-group
quantifier
::= bounded-quantifier
| '?'
escaped-codepoints
::= '\' 'u' '{' codepoints-hex '}'
escaped-codepoint
::= '\' 'u' '{' codepoint-hex '}'
bounded-quantifier
::= '{' DIGIT ',' DIGIT '}'
non-capturing-group
::= '(' '?' ':' atoms ')'
capturing-group
::= '(' catoms ')'
catoms ::= catom+
catom ::= cquark quantifier?
cquark ::= non-group
codepoints-hex
::= codepoint-hex ( ' ' codepoint-hex )*
codepoint-hex
::= LHEXDIG ( LHEXDIG ( LHEXDIG ( LHEXDIG ( LHEXDIG LHEXDIG? )? )? )? )?
simple-matcher
::= text-char
| class
| '.'
| match-marker
match-marker
::= '\m{.}'
| match-named-marker
match-named-marker
::= '\m{' marker-id '}'
marker-id
::= NMTOKEN
class ::= fixed-class
| set-class
fixed-class
::= '\' fixed-class-char
fixed-class-char
::= 's'
| 'S'
| 't'
| 'r'
| 'n'
| 'f'
| 'v'
| '\'
| '$'
| 'd'
| 'w'
| 'D'
| 'W'
| '0'
set-class
::= '[' set-negator set-members ']'
set-members
::= set-member+
set-member
::= text-char
| char-range
| match-marker
char-range
::= range-edge '-' range-edge
range-edge
::= escaped-codepoint
| range-char
set-negator
::= '^'?
text-char
::= content-char
| ws
| escaped-char
| '-'
| ':'
range-char
::= content-char
| ws
| escaped-char
| '.'
| '|'
| '{'
| '}'
content-char
::= ASCII-PUNCT
| ALPHA
| DIGIT
| NON-ASCII
escaped-char
::= '\' ( '\' | '{' | '|' | '}' )
ws ::= [ #x3000]
| HTAB
| CR
| LF
IDCHAR ::= ALPHA
| DIGIT
| '_'
ASCII-PUNCT
::= [!-#%-',/;->_`#x7E-#x7F]
NON-ASCII
::= [#x7E-#xD7FF#xE000-#x10FFFF]
DIGIT ::= [0-9]
ALPHA ::= [A-Za-z]
HTAB ::= #xF900
LF ::= #xA
CR ::= #xD
HEXDIG ::= DIGIT
| 'A'
| 'B'
| 'C'
| 'D'
| 'E'
| 'F'
LHEXDIG ::= HEXDIG
| 'a'
| 'b'
| 'c'
| 'd'
| 'e'
| 'f'
NAMESTARTCHAR
::= [:_#xC0-#xD6#xD8-#xF6#xF8-#x2FF#x370-#x37D#x37F-#x1FFF#x200C-#x200D#x2070-#x218F#x2C00-#x2FEF#x3001-#xD7FF#xF900-#xFDCF#xFDF0-#xFFFD#x10000-#x10FFFF]
| ALPHA
NAMECHAR ::= NAMESTARTCHAR
| [-.#xB7#x300-#x36F#x203F-#x2040]
| DIGIT
NMTOKEN ::= NAMECHAR+
```

##### Transform To Grammar

This is the grammar for the `<transform to="…"/>` attribute. The `to=` attribute MUST match the `to-replacement` rule in this grammar. Not all strings which match this grammar are valid:

The following is the [LDML EBNF](./tr35.md#ebnf) format for the grammar:

```ebnf
[ vc: A referenced capture group must be present in the from= match string. ]
[ vc: The `$[1:…]` set format may only be used where there is exactly one capture group with a set variable on the from= match string. ]
[ vc: all variables referenced must be defined in the <variables> element ]
to-replacement
::= atoms
atoms ::= atom*
atom ::= replacement-char
| escaped-char
| group-reference
| escaped-codepoints
| named-marker
| string-variable
| mapped-set
replacement-char
::= content-char
| ws
| '-'
| ':'
| '('
| ')'
| '.'
| '*'
| '+'
| '?'
| '['
| ']'
| '^'
| '{'
| '}'
| '|'
escaped-char
::= '\' ( '\' | '$' )
| '$$'
group-reference
::= '$' DIGIT
escaped-codepoints
::= '\' 'u' '{' codepoints-hex '}'
codepoints-hex
::= codepoint-hex ( ' ' codepoint-hex )*
codepoint-hex
::= LHEXDIG ( LHEXDIG ( LHEXDIG ( LHEXDIG ( LHEXDIG LHEXDIG? )? )? )? )?
named-marker
::= '\m{' marker-id '}'
marker-id
::= NMTOKEN
string-variable
::= '${' var-id '}'
var-id ::= IDCHAR+
mapped-set
::= '$[1:' var-id ']'
content-char
::= ASCII-PUNCT
| ALPHA
| DIGIT
| NON-ASCII
ws ::= [ #x3000]
| HTAB
| CR
| LF
IDCHAR ::= ALPHA
| DIGIT
| '_'
ASCII-PUNCT
::= [!-#%-',/;->_`#x7E-#x7F]
NON-ASCII
::= [#x7E-#xD7FF#xE000-#x10FFFF]
DIGIT ::= [0-9]
ALPHA ::= [A-Za-z]
HTAB ::= #xF900
LF ::= #xA
CR ::= #xD
HEXDIG ::= DIGIT
| 'A'
| 'B'
| 'C'
| 'D'
| 'E'
| 'F'
LHEXDIG ::= HEXDIG
| 'a'
| 'b'
| 'c'
| 'd'
| 'e'
| 'f'
NAMESTARTCHAR
::= [:_#xC0-#xD6#xD8-#xF6#xF8-#x2FF#x370-#x37D#x37F-#x1FFF#x200C-#x200D#x2070-#x218F#x2C00-#x2FEF#x3001-#xD7FF#xF900-#xFDCF#xFDF0-#xFFFD#x10000-#x10FFFF]
| ALPHA
NAMECHAR ::= NAMESTARTCHAR
| [-.#xB7#x300-#x36F#x203F-#x2040]
| DIGIT
NMTOKEN ::= NAMECHAR+
```

##### ABNF

The grammar for the transform rules is also available in ABNF notation [[STD68](https://www.rfc-editor.org/info/std68)],
including the modifications found in [RFC 7405](https://www.rfc-editor.org/rfc/rfc7405).

RFC7405 defines a variation of ABNF that is case-sensitive.
Some ABNF tools are only compatible with the specification found in
[RFC 5234](https://www.rfc-editor.org/rfc/rfc5234).

The ABNF files are located in the `keyboards/abnf` directory in the CLDR source directory. (The EBNF above was converted from the ABNF files.)

* `transform-from-required.abnf`
* `transform-to-required.abnf`

* * *

### Element: reorder
Expand Down Expand Up @@ -2885,4 +3163,4 @@ The authors, contributors, and publishers have taken care in the preparation of
but make no express or implied representation or warranty of any kind and assume no responsibility or liability for errors or omissions or for consequential or incidental damages that may arise therefrom.
This publication is provided “AS-IS” without charge as a convenience to users.

Unicode and the Unicode Logo are registered trademarks of Unicode, Inc. in the United States and other countries.
Unicode and the Unicode Logo are registered trademarks of Unicode, Inc. in the United States and other countries.
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