Simplify syntaxes

[lahmatiy]

While working on new matching approach in CSSTree I found that some syntaxes can be simplified. I wrote a script to detect some cases. Here is the output:

# mdn/atRules/@font-face "font-display"
A top level group can be omitted
Current syntax:   [ auto | block | swap | fallback | optional ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: auto | block | swap | fallback | optional
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/atRules "@import"
A single term group can be omitted and a multiplier moved to a term
Current syntax:   @import [ <string> | <url> ] [ <media-query-list> ]? ;
                                               ~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: @import [ <string> | <url> ] <media-query-list>? ;
                                               ~~~~~~~~~~~~~~~~~~~

# mdn/properties "cursor"
A top level group can be omitted
Current syntax:   [ [ <url> [ <x> <y> ]? , ]* [ auto | default | none | context-menu | help | pointer | progress | wait | cell | crosshair | text | vertical-text | alias | copy | move | no-drop | not-allowed | e-resize | n-resize | ne-resize | nw-resize | s-resize | se-resize | sw-resize | w-resize | ew-resize | ns-resize | nesw-resize | nwse-resize | col-resize | row-resize | all-scroll | zoom-in | zoom-out | grab | grabbing ] ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: [ <url> [ <x> <y> ]? , ]* [ auto | default | none | context-menu | help | pointer | progress | wait | cell | crosshair | text | vertical-text | alias | copy | move | no-drop | not-allowed | e-resize | n-resize | ne-resize | nw-resize | s-resize | se-resize | sw-resize | w-resize | ew-resize | ns-resize | nesw-resize | nwse-resize | col-resize | row-resize | all-scroll | zoom-in | zoom-out | grab | grabbing ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/properties "initial-letter-align"
A top level group can be omitted
Current syntax:   [ auto | alphabetic | hanging | ideographic ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: auto | alphabetic | hanging | ideographic
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/properties "outline"
A top level group can be omitted
Current syntax:   [ <'outline-color'> || <'outline-style'> || <'outline-width'> ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: <'outline-color'> || <'outline-style'> || <'outline-width'>
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "attr()"
A group can be omitted and a multiplier moved to a non-comma term
Current syntax:   attr( <attr-name> <type-or-unit>? [, <attr-fallback> ]? )
                                                    ~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: attr( <attr-name> <type-or-unit>? , <attr-fallback>? )
                                                    ~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "bg-position"
A top level group can be omitted
Current syntax:   [ [ left | center | right | top | bottom | <length-percentage> ] | [ left | center | right | <length-percentage> ] [ top | center | bottom | <length-percentage> ] | [ center | [ left | right ] <length-percentage>? ] && [ center | [ top | bottom ] <length-percentage>? ] ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: [ left | center | right | top | bottom | <length-percentage> ] | [ left | center | right | <length-percentage> ] [ top | center | bottom | <length-percentage> ] | [ center | [ left | right ] <length-percentage>? ] && [ center | [ top | bottom ] <length-percentage>? ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "circle()"
A single term group can be omitted and a multiplier moved to a term
Current syntax:   circle( [ <shape-radius> ]? [ at <position> ]? )
                          ~~~~~~~~~~~~~~~~~~~
Suggested syntax: circle( <shape-radius>? [ at <position> ]? )
                          ~~~~~~~~~~~~~~~

# mdn/syntaxes "common-lig-values"
A top level group can be omitted
Current syntax:   [ common-ligatures | no-common-ligatures ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: common-ligatures | no-common-ligatures
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "contextual-alt-values"
A top level group can be omitted
Current syntax:   [ contextual | no-contextual ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: contextual | no-contextual
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "contrast()"
A single term group with no multiplier can be omitted
Current syntax:   contrast( [ <number-percentage> ] )
                            ~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: contrast( <number-percentage> )
                            ~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "discretionary-lig-values"
A top level group can be omitted
Current syntax:   [ discretionary-ligatures | no-discretionary-ligatures ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: discretionary-ligatures | no-discretionary-ligatures
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "east-asian-variant-values"
A top level group can be omitted
Current syntax:   [ jis78 | jis83 | jis90 | jis04 | simplified | traditional ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: jis78 | jis83 | jis90 | jis04 | simplified | traditional
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "east-asian-width-values"
A top level group can be omitted
Current syntax:   [ full-width | proportional-width ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: full-width | proportional-width
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "fixed-repeat"
A single term group with no multiplier can be omitted
Current syntax:   repeat( [ <positive-integer> ] , [ <line-names>? <fixed-size> ]+ <line-names>? )
                          ~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: repeat( <positive-integer> , [ <line-names>? <fixed-size> ]+ <line-names>? )
                          ~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "font-variant-css21"
A top level group can be omitted
Current syntax:   [ normal | small-caps ]
                  ~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: normal | small-caps
                  ~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "historical-lig-values"
A top level group can be omitted
Current syntax:   [ historical-ligatures | no-historical-ligatures ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: historical-ligatures | no-historical-ligatures
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "matrix()"
A sequence can be rolled up
Current syntax:   matrix( <number> [, <number> ]{5} )
                          ~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: matrix( <number>#{6} )
                          ~~~~~~~~~~~~

# mdn/syntaxes "matrix3d()"
A sequence can be rolled up
Current syntax:   matrix3d( <number> [, <number> ]{15} )
                            ~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: matrix3d( <number>#{16} )
                            ~~~~~~~~~~~~~

# mdn/syntaxes "numeric-figure-values"
A top level group can be omitted
Current syntax:   [ lining-nums | oldstyle-nums ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: lining-nums | oldstyle-nums
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "numeric-fraction-values"
A top level group can be omitted
Current syntax:   [ diagonal-fractions | stacked-fractions ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: diagonal-fractions | stacked-fractions
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "numeric-spacing-values"
A top level group can be omitted
Current syntax:   [ proportional-nums | tabular-nums ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: proportional-nums | tabular-nums
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "opacity()"
A single term group with no multiplier can be omitted
Current syntax:   opacity( [ <number-percentage> ] )
                           ~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: opacity( <number-percentage> )
                           ~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "position"
A top level group can be omitted
Current syntax:   [ [ left | center | right ] || [ top | center | bottom ] | [ left | center | right | <length-percentage> ] [ top | center | bottom | <length-percentage> ]? | [ [ left | right ] <length-percentage> ] && [ [ top | bottom ] <length-percentage> ] ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: [ left | center | right ] || [ top | center | bottom ] | [ left | center | right | <length-percentage> ] [ top | center | bottom | <length-percentage> ]? | [ [ left | right ] <length-percentage> ] && [ [ top | bottom ] <length-percentage> ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "scale()"
A sequence can be rolled up
Current syntax:   scale( <number> [, <number> ]? )
                         ~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: scale( <number>#{1,2} )
                         ~~~~~~~~~~~~~~

# mdn/syntaxes "skew()"
A sequence can be rolled up
Current syntax:   skew( <angle> [, <angle> ]? )
                        ~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: skew( <angle>#{1,2} )
                        ~~~~~~~~~~~~~

# mdn/syntaxes "shadow-t"
A top level group can be omitted
Current syntax:   [ <length>{2,3} && <color>? ]
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: <length>{2,3} && <color>?
                  ~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "step-timing-function"
A group can be omitted and a multiplier moved to a non-comma term
Current syntax:   step-start | step-end | steps( <integer> [, [ start | end ] ]? )
                                                           ~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: step-start | step-end | steps( <integer> , [ start | end ]? )
                                                           ~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "track-repeat"
A single term group with no multiplier can be omitted
Current syntax:   repeat( [ <positive-integer> ] , [ <line-names>? <track-size> ]+ <line-names>? )
                          ~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: repeat( <positive-integer> , [ <line-names>? <track-size> ]+ <line-names>? )
                          ~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "translate()"
A sequence can be rolled up
Current syntax:   translate( <length-percentage> [, <length-percentage> ]? )
                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: translate( <length-percentage>#{1,2} )
                             ~~~~~~~~~~~~~~~~~~~~~~~~~

# mdn/syntaxes "var()"
A group can be omitted and a multiplier moved to a non-comma term
Current syntax:   var( <custom-property-name> [, <declaration-value> ]? )
                                              ~~~~~~~~~~~~~~~~~~~~~~~~~
Suggested syntax: var( <custom-property-name> , <declaration-value>? )
                                              ~~~~~~~~~~~~~~~~~~~~~~


Total suggestions: 31
   17 × A top level group can be omitted
    2 × A single term group can be omitted and a multiplier moved to a term
    5 × A sequence can be rolled up
    4 × A single term group with no multiplier can be omitted
    3 × A group can be omitted and a multiplier moved to a non-comma term

Action plan:

• mdn/data specific syntaxes (generated by a description) can be changed quite easily
• Some syntaxes are already changed in related specs, but mdn/data contains its outdated versions – those syntaxes should be aligned to specs
• Some syntaxes are defined in that form in specs (such as matrix(), skew(), repeat(), attr() etc) – issues to related specs should be filled and syntaxes updated depending on its resolution

//cc @fantasai @tabatkins (sorry for mentioning, but I thought it might be interesting to you)

[tabatkins]

Yeah, all these changes are correct, and I'd accept PRs on the relevant specs to change them.