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[css] Value definition parser
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From: Bjoern H. <der...@gm...> - 2003-07-27 03:34:50
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Hi Robin,
I wrote a hackerish parser for the property value definitions used in
the CSS and SVG specifications. For example for the font property in CSS
2.1
[ [ <'font-style'> || <'font-variant'> || <'font-weight'> ]?
<'font-size'> [ / <'line-height'> ]? <'font-family'> ] | caption |
icon | menu | message-box | small-caption | status-bar | inherit
which would parse to a hash reference like (XML::Simple::XMLout
rootname => 'val'):
<val typ="Disjunction" min="1" max="1">
<val typ="Sequence" min="1" max="1">
<val typ="Conjunction" min="0" max="1">
<val min="1" val="<'font-style'>" max="1" />
<val min="1" val="<'font-variant'>" max="1" />
<val min="1" val="<'font-weight'>" max="1" />
</val>
<val min="1" val="<'font-size'>" max="1" />
<val typ="Sequence" min="0" max="1">
<val min="1" val="/" max="1" />
<val min="1" val="<'line-height'>" max="1" />
</val>
<val min="1" val="<'font-family'>" max="1" />
</val>
<val min="1" val="caption" max="1" />
<val min="1" val="icon" max="1" />
<val min="1" val="menu" max="1" />
<val min="1" val="message-box" max="1" />
<val min="1" val="small-caption" max="1" />
<val min="1" val="status-bar" max="1" />
<val min="1" val="inherit" max="1" />
</val>
This enables a secondary module with more knowledge of properties to
resolve this definition to
<val typ="Disjunction" min="1" max="1">
<val typ="Sequence" min="1" max="1">
<val typ="Conjunction" min="0" max="1">
<val typ="Disjunction" min="1" max="1">
<val min="1" val="normal" max="1" />
<val min="1" val="italic" max="1" />
<val min="1" val="oblique" max="1" />
</val>
<val typ="Disjunction" min="1" max="1">
<val min="1" val="normal" max="1" />
<val min="1" val="small-caps" max="1" />
</val>
<val typ="Disjunction" min="1" max="1">
<val min="1" val="normal" max="1" />
<val min="1" val="bold" max="1" />
<val min="1" val="bolder" max="1" />
<val min="1" val="lighter" max="1" />
<val min="1" val="100" max="1" />
<val min="1" val="200" max="1" />
<val min="1" val="300" max="1" />
<val min="1" val="400" max="1" />
<val min="1" val="500" max="1" />
<val min="1" val="600" max="1" />
<val min="1" val="700" max="1" />
<val min="1" val="800" max="1" />
<val min="1" val="900" max="1" />
</val>
</val>
<val typ="Disjunction" min="1" max="1">
<val min="1" val="xx-small" max="1" />
<val min="1" val="x-small" max="1" />
<val min="1" val="small" max="1" />
<val min="1" val="medium" max="1" />
<val min="1" val="large" max="1" />
<val min="1" val="x-large" max="1" />
<val min="1" val="xx-large" max="1" />
<val min="1" val="larger" max="1" />
<val min="1" val="smaller" max="1" />
<val min="1" val="<length>" max="1" />
<val min="1" val="<percentage>" max="1" />
</val>
<val typ="Sequence" min="0" max="1">
<val min="1" val="/" max="1" />
<val typ="Disjunction" min="1" max="1">
<val min="1" val="normal" max="1" />
<val min="1" val="<integer>" max="1" />
<val min="1" val="<real>" max="1" />
<val min="1" val="<length>" max="1" />
<val min="1" val="<percentage>" max="1" />
</val>
</val>
<val typ="Disjunction" min="1" max="1">
<val typ="Sequence" min="1" max="1">
<val typ="Disjunction" min="1" max="1">
<val min="1" val="<identifier>" max="-1" />
<val min="1" val="<string>" max="1" />
<val min="1" val="serif" max="1" />
<val min="1" val="sans-serif" max="1" />
<val min="1" val="cursive" max="1" />
<val min="1" val="fantasy" max="1" />
<val min="1" val="monospace" max="1" />
</val>
<val typ="Disjunction" min="0" max="-1">
<val typ="Sequence" min="1" max="1">
<val min="1" val="," max="1" />
<val typ="Disjunction" min="1" max="1">
<val min="1" val="<identifier>" max="-1" />
<val min="1" val="<string>" max="1" />
</val>
</val>
<val min="1" val="serif" max="1" />
<val min="1" val="sans-serif" max="1" />
<val min="1" val="cursive" max="1" />
<val min="1" val="fantasy" max="1" />
<val min="1" val="monospace" max="1" />
</val>
</val>
</val>
</val>
<val min="1" val="caption" max="1" />
<val min="1" val="icon" max="1" />
<val min="1" val="menu" max="1" />
<val min="1" val="message-box" max="1" />
<val min="1" val="small-caption" max="1" />
<val min="1" val="status-bar" max="1" />
<val min="1" val="inherit" max="1" />
</val>
(Yes, font is complex :-) (Note that <length> is not yet expanded.
That's however probably mandatory if there are differences between
CSS/SVG versions, profiles, etc.)
I wrote a module that performs this operation but it is not an alpha
yet. There are also issues with the value definitions, for example
'font-size' does not allow negative values while 'left' does but both
refer only to <length> in their definitions. The final goal is to write
a CSS::Validator module that takes such a syntax tree and validates the
LexicalValueList provided by CSS::SAC for a property against it. That's
quite easy as the values are supposed to represent single LexicalUnits
and all a validator has to do would be to check $lu->is_type(INTEGER)
for example. What I've got so far is able to tell you
a > b + c ~ d e
{
font: inherit; -- valid
font: invalid; -- invalid
font: normal small-caps 3em/3 Verdana, sans-serif; -- valid
color: red; -- valid
unknown: foo; -- unknown
}
The major benefit of this approach is that the validator can easily be
extended for new or custom profiles without writing any code. Users
would for example be able to write a profile for a specific browser and
have a SAC filter that excludes all unsupported properties or for a
validator that warns about their use. Or they could validate proprietary
extensions like the -moz-* or mso-* properties. That much about long
term goals...
For the parser, could you suggest a name? I've called it
My::CSS::ValueDefParser but I am sure there is room for improvement. It
should also make sense when used in combination with a module that
resolves the property references like <'font-size'> and macros like
<absolute-length> with more knowledge of a given CSS profile.
May I add it to the CVS repository? Anything to note about the best
location for it or anything else? As I've said, it's quite hackerish and
slow (based on Parse::RecDescent by the way) but it does what it is
supposed to.
PS: Any progress wrt Sourceforge CVS access? If not, it would be nice to
have what you got so far, it could then commit it to CVS.
regards.
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