Maciej Stachowiak wrote:
On May 5, 2008, at 2:13 PM, Lachlan Hunt wrote:
Define the methods to behave as if an implicit :scope selector and
descendant combinator were prepended to each selector in the group.
... Consider the following selector:
">strong, >em"
The expectation would be for this to become:
":scope >strong, :scope >em"
The question is how to parse and convert it.
... then prepending ":scope " and inserting " :scope " after every
comma before parsing would work. I believe this is currently true of
Selectors, though it may change in the future. I would guess the only
likely place for commas to appear would be in parameters to
function-like pseudo-classes, in which case the algorithm above but
excluding commas nested inside parentheses would be more
future-proof. Detail of the algorithm:
1. Initialize nesting level to 0
2. Initialize the output string to the empty string
3. While characters in the input string remain:
3.a. read the current character
3.b. if the current character is:
",": if the nesting level is 0, append ", :scope " to the output
string
"(": increase the nesting level by 1, and append "(" to the
output string
")": decrease the nesting level by 1, and append ")" to the
output string
anything else: append the current character to the output string
3.c. advance to the next character
4. return the output string
I started looking into this for the possibility of introducing
queryScopedSelector(), or similar, into version 2, but it seems that
this proposed pre-parse doesn't handle enough cases to be relible enough.
The solution would need to handle all of the following more complex
cases involving escaped chars:
span[title="\""]
span[title='\'']
span[title="\\"]
span[title=\"\(\)]
span[title=\'\"]
div:foo(x,y)
div:foo(\(\))
Plus many other varations.
One possible solution would be to define that it uses a slightly
modified grammar from ordinary Selectors. It would have everything the
same, except that the selector production would become:
selector
: combinator? simple_selector_sequence [ combinator
simple_selector_sequence ]*
;
http://www.w3.org/TR/css3-selectors/#w3cselgrammar
Then instead of requiring a pre-parse, inserting :scope and then parsing
with the normal selector parser, implementations would modify their
selector parsers to handle the optional combinator at the beginning and
then I would define that :scope (or equivalent) is to be implied at the
beginning of each selector.
Another solution is to use a slightly more complicated pre-parse than
the one proposed above. I believe the following would work, unless I
made a mistake.
1. Initialise nesting level to 0
2. Initialise the output string to the empty string
3. Initialise the escape flag to false
4. Begin tokenising in the Normal state
Normal state:
Consume the next input character
-> U+002C COMMA ","
If the escape flag is true, append "," to the output string and
set the flag to false
Otherwise, if the nesting level is 0, append ", :scope " to the
output string
Otherwise, treat it as per the "anything else" entry below.
-> U+0022 QUOTATION MARK '"'
Append '"' to the output string
If the escape flag is true, set the flag to false
Otherwise, switch to the Double-quoted string state
-> U+0027 APOSTROPHE "'"
Append "'" to the output string
If the escape flag is true, set the flag to false
Otherwise, switch to the Single-quoted string state
-> U+0028 LEFT PARENTHESIS "("
Append "(" to the output string
If the escape flag is true, set the flag to false
Otherwise, increase the nesting level by 1
-> U+0029 RIGHT PARENTHESIS "("
Append "(" to the output string
If the escape flag is true, set the flag to false
Otherwise, if the nesting level is greater than zero, decrease by 1
-> U+005C REVERSE SOLIDUS "\"
Append "\" to the output string
If the escape flag is true, set the flag to false
Otherwise, set the escape flag to true
-> EOF
Return the output string
-> Anything Else
If the escape flag is true, set the flag to false
Append the current character to the output string
Double-quoted string state:
Consume the next input character
-> U+005C REVERSE SOLIDUS "\"
Append "\" to the output string
If the escape flag is true, set the flag to false
Otherwise, set the escape flag to true
-> U+0022 QUOTATION MARK '"'
Append '"' to the output string
If the escape flag is true, set the flag to false
Otherwise, switch to the Normal state
-> Anything Else
Append the current character to the output string
Single-quoted string state:
Consume the next input character
-> U+005C REVERSE SOLIDUS "\"
Append "\" to the output string
If the escape flag is true, set the flag to false
Otherwise, set the escape flag to true
-> U+0027 APOSTROPHE "'"
Append "'" to the output string
If the escape flag is true, set the flag to false
Otherwise, switch to the Normal state
-> Anything Else
Append the current character to the output string
If the escape flag is true, set the flag to false
--
Lachlan Hunt - Opera Software
http://lachy.id.au/
http://www.opera.com/
