The grammar below defines the syntax of CSS 2.1. It is in some sense,however, a superset of CSS 2.1 as this specification imposes additionalsemantic constraints not expressed in this grammar. A conforming UAmust also adhere to theforward-compatible parsing rules, the selectors notation, theproperty and value notation,and the unit notation. However, not all syntactically correct CSS can takeeffect, since the document language may impose restrictions that arenot in CSS, e.g., HTML imposes restrictions on the possible values ofthe "class" attribute.
The grammar below is
The productions are:
stylesheet : [ CHARSET_SYM STRING ';' ]? [S|CDO|CDC]* [ import [S|CDO|CDC]* ]* [ [ ruleset | media | page ] [S|CDO|CDC]* ]* ;import : IMPORT_SYM S* [STRING|URI] S* [ medium [ COMMA S* medium]* ]? ';' S* ;media : MEDIA_SYM S* medium [ COMMA S* medium ]* LBRACE S* ruleset* '}' S* ;medium : IDENT S* ;page : PAGE_SYM S* pseudo_page? S* LBRACE S* declaration [ ';' S* declaration ]* '}' S* ;pseudo_page : ':' IDENT ;operator : '/' S* | COMMA S* | /* empty */ ;combinator : PLUS S* | GREATER S* | S ;unary_operator : '-' | PLUS ;property : IDENT S* ;ruleset : selector [ COMMA S* selector ]* LBRACE S* declaration [ ';' S* declaration ]* '}' S* ;selector : simple_selector [ combinator simple_selector ]* ;simple_selector : element_name [ HASH | class | attrib | pseudo ]* | [ HASH | class | attrib | pseudo ]+ ;class : '.' IDENT ;element_name : IDENT | '*' ;attrib : '[' S* IDENT S* [ [ '=' | INCLUDES | DASHMATCH ] S* [ IDENT | STRING ] S* ]? ']' ;pseudo : ':' [ IDENT | FUNCTION S* IDENT? S* ')' ] ;declaration : property ':' S* expr prio? | /* empty */ ;prio : IMPORTANT_SYM S* ;expr : term [ operator term ]* ;term : unary_operator? [ NUMBER S* | PERCENTAGE S* | LENGTH S* | EMS S* | EXS S* | ANGLE S* | TIME S* | FREQ S* ] | STRING S* | IDENT S* | URI S* | hexcolor | function ;function : FUNCTION S* expr ')' S* ;/* * There is a constraint on thecolor that it must * have either 3 or 6 hex-digits (i.e., [0-9a-fA-F]) * after the "#"; e.g., "#000" is OK, but "#abcd" is not. */hexcolor : HASH S* ;
The following is the
The two occurrences of "\377" represent the highest characternumber that current versions of Flex can deal with (decimal 255). Theyshould be read as "\4177777" (decimal 1114111), which is the highestpossible code point in
%option case-insensitiveh[0-9a-f]nonascii[\200-\377]unicode\\{h}{1,6}(\r\n|[ \t\r\n\f])?escape{unicode}|\\[^\r\n\f0-9a-f]nmstart[_a-z]|{nonascii}|{escape}nmchar[_a-z0-9-]|{nonascii}|{escape}string1\"([^\n\r\f\\"]|\\{nl}|{escape})*\"string2\'([^\n\r\f\\']|\\{nl}|{escape})*\'invalid1\"([^\n\r\f\\"]|\\{nl}|{escape})*invalid2\'([^\n\r\f\\']|\\{nl}|{escape})*comment\/\*[^*]*\*+([^/*][^*]*\*+)*\/ident-?{nmstart}{nmchar}*name{nmchar}+num[0-9]+|[0-9]*"."[0-9]+string{string1}|{string2}invalid{invalid1}|{invalid2}url([!#$%&*-~]|{nonascii}|{escape})*s[ \t\r\n\f]+w{s}?nl\n|\r\n|\r|\fAa|\\0{0,4}(41|61)(\r\n|[ \t\r\n\f])?Cc|\\0{0,4}(43|63)(\r\n|[ \t\r\n\f])?Dd|\\0{0,4}(44|64)(\r\n|[ \t\r\n\f])?Ee|\\0{0,4}(45|65)(\r\n|[ \t\r\n\f])?Gg|\\0{0,4}(47|67)(\r\n|[ \t\r\n\f])?|\\gHh|\\0{0,4}(48|68)(\r\n|[ \t\r\n\f])?|\\hIi|\\0{0,4}(49|69)(\r\n|[ \t\r\n\f])?|\\iKk|\\0{0,4}(4b|6b)(\r\n|[ \t\r\n\f])?|\\kMm|\\0{0,4}(4d|6d)(\r\n|[ \t\r\n\f])?|\\mNn|\\0{0,4}(4e|6e)(\r\n|[ \t\r\n\f])?|\\nOo|\\0{0,4}(51|71)(\r\n|[ \t\r\n\f])?|\\oPp|\\0{0,4}(50|70)(\r\n|[ \t\r\n\f])?|\\pRr|\\0{0,4}(52|72)(\r\n|[ \t\r\n\f])?|\\rSs|\\0{0,4}(53|73)(\r\n|[ \t\r\n\f])?|\\sTt|\\0{0,4}(54|74)(\r\n|[ \t\r\n\f])?|\\tXx|\\0{0,4}(58|78)(\r\n|[ \t\r\n\f])?|\\xZz|\\0{0,4}(5a|7a)(\r\n|[ \t\r\n\f])?|\\z%%{s}{return S;}\/\*[^*]*\*+([^/*][^*]*\*+)*\//* ignore comments */{s}+\/\*[^*]*\*+([^/*][^*]*\*+)*\/{unput(' '); /*replace by space*/}"<!--"{return CDO;}"-->"{return CDC;}"~="{return INCLUDES;}"|="{return DASHMATCH;}{w}"{"{return LBRACE;}{w}"+"{return PLUS;}{w}">"{return GREATER;}{w}","{return COMMA;}{string}{return STRING;}{invalid}{return INVALID; /* unclosed string */}{ident}{return IDENT;}"#"{name}{return HASH;}@{I}{M}{P}{O}{R}{T}{return IMPORT_SYM;}@{P}{A}{G}{E}{return PAGE_SYM;}@{M}{E}{D}{I}{A}{return MEDIA_SYM;}@{C}{H}{A}{R}{S}{E}{T}{return CHARSET_SYM;}"!"({w}|{comment})*{I}{M}{P}{O}{R}{T}{A}{N}{T}{return IMPORTANT_SYM;}{num}{E}{M}{return EMS;}{num}{E}{X}{return EXS;}{num}{P}{X}{return LENGTH;}{num}{C}{M}{return LENGTH;}{num}{M}{M}{return LENGTH;}{num}{I}{N}{return LENGTH;}{num}{P}{T}{return LENGTH;}{num}{P}{C}{return LENGTH;}{num}{D}{E}{G}{return ANGLE;}{num}{R}{A}{D}{return ANGLE;}{num}{G}{R}{A}{D}{return ANGLE;}{num}{M}{S}{return TIME;}{num}{S}{return TIME;}{num}{H}{Z}{return FREQ;}{num}{K}{H}{Z}{return FREQ;}{num}{ident}{return DIMENSION;}{num}%{return PERCENTAGE;}{num}{return NUMBER;}"url("{w}{string}{w}")"{return URI;}"url("{w}{url}{w}")"{return URI;}{ident}"("{return FUNCTION;}.{return *yytext;}There are some differences in the syntax specified in the CSS1recommendation ([CSS1]), and the one above. Most of these are dueto new tokens in CSS2 that didn't exist in CSS1. Others are becausethe grammar has been rewritten to be more readable. However, there aresome incompatible changes, that were felt to be errors in the CSS1syntax. They are explained below.