W3C-CSS(2) W3C-CSS(2)
NAME
w3c-css - cascading style sheet parser
SYNOPSIS
include "css.m";
css := load CSS CSS->PATH;
Stylesheet: adt {
charset: string;
imports: list of ref Import;
statements: list of ref Statement;
};
Import: adt {
name: string;
media: list of string;
};
Statement: adt {
pick{
Media =>
media: list of string;
rules: list of ref Statement.Ruleset;
Page =>
pseudo: string;
decls: list of ref Decl;
Ruleset =>
selectors: list of Selector;
decls: list of ref Decl;
}
};
Decl: adt {
property: string;
values: list of ref Value;
important: int;
};
Selector: type list of (int, Simplesel); # (combinator, simplesel)
Simplesel: type list of ref Select;
Select: adt {
name: string;
pick{
Element or ID or Any or Class or Pseudo =>
# empty
Attrib =>
op: string; # "=" "~=" "|="
value: ref Value; # optional Ident or String
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Pseudofn =>
arg: string;
}
};
Value: adt {
sep: int; # operator preceding this term
pick{
String or
Number or
Percentage or
Url or
Unicoderange =>
value: string;
Hexcolour =>
value: string; # as given
rgb: (int, int, int); # converted
RGB =>
args: cyclic list of ref Value; # as given
rgb: (int, int, int); # converted
Ident =>
name: string;
Unit =>
value: string; # int or float
units: string; # suffix giving units
Function =>
name: string;
args: cyclic list of ref Value;
}
};
init: fn(diag: int);
parse: fn(s: string): (ref Stylesheet, string);
parsedecl: fn(s: string): (list of ref Decl, string);
DESCRIPTION
Css implements a parser for the World-Wide Web Consortium's
Cascading Style Sheet, specification 2.1.
Init must be called before any other operation in the mod-
ule. If diag is non-zero, the module will print diagnostics
on standard output for malformed or unrecognised items that
are ignored during parsing (as required by the specifica-
tion).
Parse takes a complete stylesheet in string s, parses it,
and returns a tuple (sheet, err) where sheet refers to a
Stylesheet value containing the logical content of s, as
described below. On a fatal error, sheet is nil and err is
a diagnostic. Most syntactic errors are ignored, as the
specification requires.
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In some applications there can be auxiliary declarations
outside a stylesheet. Parsedecl takes a string s containing
a sequence of declarations, and returns a tuple (decls, err)
where decls is a list of references to Decl values, each
representing a single declaration in s. On a fatal error,
decls is nil, and err is a diagnostic.
The adts represent an abstract syntax of the CSS grammar.
The concrete syntax is presented below in an extended BNF,
derived from the reference grammar, with each section
labelled by the name of the corresponding adts. (Compared
to the reference grammar in the specification, it abstracts
away from the complex rules about where whitespace can
appear.)
Stylesheet
stylesheet ::= [ '@charset' STRING ';' ] import* statement*
Limbo lists represent lists of items in the grammar.
Nil values denote optional components that are missing.
Upper-case names such as IDENT, STRING and NUMBER are
terminals; see the CSS specification for their often
subtle definitions. They are usually represented by
Limbo string values in the adts.
Import
import ::= '@import' (STRING|uri) [medium (',' medium)*] ';'
uri ::= 'url(' STRING ')'
Import.name holds the text of the STRING or uri.
Statement
statement ::= ruleset | media | page
media ::= '@media' medium (',' medium)* '{' ruleset* '}'
medium ::= IDENT
page ::= '@page' [pseudo_page] '{' declaration (';' declaration)* '}'
pseudo_page ::= ':' IDENT
ruleset ::= selector (',' selector)* '{' declaration (';' declaration)* '}'
Statement is not in the reference grammar, but is
introduced here to give a name corresponding to the
pick adt.
Decl
declaration ::= property ':' expr ['!' 'important'] | /* empty */
property ::= IDENT
Decl.values is a list representing the terms of the
expr (see below for details). Decl's field important
is non-zero if the optional `important' priority is
given.
list of ref Value
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expr ::= term (operator term)*
operator ::= '/' | ',' | /* empty */
An expr is always represented as a list of references
to Value in some containing structure (where Value rep-
resents a term, see below). The operator preceding
each term appears as the field sep of the corresponding
Value, where a space character represents `empty' (con-
catenation).
Selector
selector ::= simple_selector (combinator simple_selector)*
combinator ::= '+' | '>' | /* empty */
Selector is just a type synonym for a list of tuples,
say (com, simplesel) where the simplesel value repre-
sents simple_selector (see below), and the integer com
is one of the characters space (representing `empty'),
`>' or `+', giving the combinator that preceded the
simple selector. (The first in the list is always
space.)
Simplesel, Select
simple_selector ::= element_name (hash | class | attrib | pseudo)*
| (hash | class | attrib | pseudo)+
hash ::= '#' NAME
class ::= '.' IDENT
element_name ::= IDENT | '*'
attrib ::= '[' IDENT [('=' | '|=' | '~=') (IDENT | STRING)] ']'
pseudo ::= ':' ( IDENT | IDENT '(' [IDENT] ')' )
A simple_selector is represented by Simplesel, a list
of references to Select values, each representing one
element_name or qualifier. An element_name is repre-
sented by Select.Element for an IDENT, or Select.Any
for `*'. The qualifiers are hash (Select.ID), class
(Select.Class), attrib (Select.Attrib, where the com-
parison operator is the string op), pseudo (either
Select.Pseudo if a plain identifier, or Select.Pseudofn
for a function with optional parameter).
Value
term ::= ['+' | '-'] (NUMBER | percent | unit) | STRING | IDENT | uri | function | hexcolour | rgb
function ::= IDENT '(' expr ')'
hash ::= '#' NAME
hexcolour ::= '#' HEXDIGIT+
percent ::= NUMBER '%'
unit ::= NUMBER STRING
rgb ::= 'rgb(' term ',' term ',' term ')'
uri ::= 'url(' STRING ')'
Any sign before a Number, Percentage or Unit appears as
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the first character of value. All the dimensional
units (LENGTH, EMS, EXS, ANGLE, TIME, FREQ and others)
in the reference grammar are mapped to Value.Unit, with
the field units containing the name of the relevant
unit (eg, `cm', `in', etc.) in lower case. Values and
names appear shorn of the surrounding punctuation.
Value.Hexcolour includes the original sequence of hex
digits as a string, and a decoding of it as an rgb tri-
ple. The arguments to the CSS rgb function are simi-
larly presented in original and decoded forms, in
Value.RGB. Other function references are returned
uninterpreted in Value.Function.
SOURCE
/appl/lib/w3c/css.b
SEE ALSO
``Cascading Style Sheets, level 2 revision 1'',
http://www.w3.org/TR/CSS21
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