CSS Spec Implementation

Question

I just had a case where it would have been really useful if there were a CSS selector like :numeral. I could then make all the numerals superscript and change their color.

It then occurred to me that it would be even more useful to have something like :regex('...') which would allow me to use regex to select particular text (numerals preceded by a space, for example: :regex(' \\d*')).

Is there a good reason this sort of selection should not be implemented in CSS Spec?

@Steeven: Re your suggested edit, "if there were" is the correct construction (it's the "subjunctive" or "speculative" tense). — T.J. Crowder
– T.J. Crowder, Commented Jul 5, 2011 at 15:36

thirtydot · Accepted Answer · 2011-07-05 15:17:55Z

3

Is there a good reason this sort of selection should not be implemented in CSS Spec?

Yes - performance reasons.

A common request is a "parent selector" (similar to jQuery's :has() selector), which is also rejected for similar performance reasons.

A good read on this subject is: http://snook.ca/archives/html_and_css/css-parent-selectors

The sheer length of that article is why I'm not attempting to explain this myself.

If a parent selector is too bad from a performance viewpoint, you can imagine that a "regex selector" would be unthinkable.

Especially when you consider that not all regexes are equal: it's very easy to make very slow regexes.

For example: http://www.regular-expressions.info/catastrophic.html

edited Jul 5, 2011 at 15:17

answered Jul 5, 2011 at 15:12

thirtydot

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8 Comments

BoltClock Over a year ago

Trying to find sources citing the reason why the :contains() pseudo-class was dropped, but to no avail.

thirtydot Over a year ago

@BoltClock: 6.6.6 eh? stackoverflow.com/questions/4781141/…

T.J. Crowder Over a year ago

Parent selectors and a :regex selector are fundamentally different, I wouldn't generalize from performance aspects of the one to comment on performance aspects of the other.

jcuenod Over a year ago

This is true, partially. I disagree in that the scope of supported regex could be reduced to avoid "catastrophes" (although having said that, I question it to some degree). Nevertheless, the problem with parent (ancestor) selectors - with which I am familiar - is that later dom affects earlier rendering. This is not the case with regex because it has to match an expression.

thirtydot Over a year ago

@T.J. Crowder: I agree that my reasoning is faulty. I just went with what I could think of :( I am at least correct with the "performance" idea in my answer, see the red text in an older revision of the CSS3 spec. If :contains has "performance issues", then :regex would be much, much worse.

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