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 the color 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*
  ;

G.2 Lexical scanner

The following is the tokenizer, written in Flex (see [FLEX]) notation. The tokenizer is case-insensitive.

The two occurrences of "\377" represent the highest character number that current versions of Flex can deal with (decimal 255). They should be read as "\4177777" (decimal 1114111), which is the highest possible code point in Unicode/ISO-10646.

%option case-insensitive

h		[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|\f

A		a|\\0{0,4}(41|61)(\r\n|[ \t\r\n\f])?
C		c|\\0{0,4}(43|63)(\r\n|[ \t\r\n\f])?
D		d|\\0{0,4}(44|64)(\r\n|[ \t\r\n\f])?
E		e|\\0{0,4}(45|65)(\r\n|[ \t\r\n\f])?
G		g|\\0{0,4}(47|67)(\r\n|[ \t\r\n\f])?|\\g
H		h|\\0{0,4}(48|68)(\r\n|[ \t\r\n\f])?|\\h
I		i|\\0{0,4}(49|69)(\r\n|[ \t\r\n\f])?|\\i
K		k|\\0{0,4}(4b|6b)(\r\n|[ \t\r\n\f])?|\\k
M		m|\\0{0,4}(4d|6d)(\r\n|[ \t\r\n\f])?|\\m
N		n|\\0{0,4}(4e|6e)(\r\n|[ \t\r\n\f])?|\\n
P		p|\\0{0,4}(50|70)(\r\n|[ \t\r\n\f])?|\\p
R		r|\\0{0,4}(52|72)(\r\n|[ \t\r\n\f])?|\\r
S		s|\\0{0,4}(53|73)(\r\n|[ \t\r\n\f])?|\\s
T		t|\\0{0,4}(54|74)(\r\n|[ \t\r\n\f])?|\\t
X		x|\\0{0,4}(58|78)(\r\n|[ \t\r\n\f])?|\\x
Z		z|\\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;}

"@import"		{return IMPORT_SYM;}
"@page"			{return PAGE_SYM;}
"@media"		{return MEDIA_SYM;}
"@charset "		{return CHARSET_SYM;}

"!"({w}|{comment})*"important"	{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;}