This release improves syntax matching by new features and some fixes.

Bracketed range notation

A couple month ago bracketed range notation was added to Values and Units spec. The notation allows restrict numeric values to some range. For example, <integer [0,∞]> is for positive integers, or <number [0,1]> that can be used for an alpha value.

Since the notation is new thing in syntax definition, it isn't used in specs yet. However, there is a PR (w3c/csswg-drafts#3894) that will bring it to some specs. And CSSTree is ready for this.

Right now, the notation helped to remove <number-zero-one>, <number-one-or-greater> and <positive-integer> from generic types and define them using a regular grammar (thanks to the notation).

Low priority type matching

There are at least two productions that has a low priority in matching. It means that such productions give a chance for other production to claim a token, and if no one – claim a token. This release introduce a solution for such productions. It's hardcoded at the moment, but can be exposed if needed (i.e. if there are more such productions).

First production is <custom-ident>. The Values and Units spec states:

When parsing positionally-ambiguous keywords in a property value, a <custom-ident> production can only claim the keyword if no other unfulfilled production can claim it.

This rule takes place in properties like <'animation'>, <'transition'> and <'list-style'>. Before solves in different ways:

• <'animation'> – that's not an issue since <'custom-ident'> goes last, however a terms order can be changed in the future
• <'transition'> – there was a patch for <single-transition> that changes order of terms
• <'list-style'> – had no fixes, just didn't work in some cases (see #101)

And now, all those and the rest syntaxes work as expected.

Second production is a bit tricky. It's about "unitless zero" for <length> production. The spec states:

... if a 0 could be parsed as either a <number> or a <length> in a property (such as line-height), it must parse as a <number>.

This rule takes place in properties like <'line-height'> or <'flex'>. And now it works per spec too (try it here):

Changes

• Bumped mdn/data to 2.0.4 (#99)
• Lexer
  • Added bracketed range notation support and related refactoring
  • Removed <number-zero-one>, <number-one-or-greater> and <positive-integer> from generic types. In fact, types moved to patch, because those types can be expressed in a regular grammar due to bracketed range notation implemented
  • Added support for multiple token string matching
  • Improved <custom-ident> production matching to claim the keyword only if no other unfulfilled production can claim it (#101)
  • Improved <length> production matching to claim "unitless zero" only if no other unfulfilled production can claim it
  • Changed lexer's constructor to prevent generic types override when used
  • Fixed large ||- and &&-group matching, matching continues from the beginning on term match (#85)
  • Fixed checking that value has var() occurrences when value is a string (such values can't be matched on syntax currently and fail with specific error that can be used for ignorance in validation tools)
  • Fixed <declaration-value> and <any-value> matching when a value contains a function, parentheses or braces