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Re: Selecting Preceding Elements

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Thu, 28 Oct 2010 07:15:59 -0700
Message-ID: <AANLkTin1++8W9urh5-bkz6k1ETCjseNQxe_sRPd_iVgR@mail.gmail.com>
To: Nathan Hammond <w3.org@nathanhammond.com>
Cc: www-style@w3.org
On Tue, Sep 28, 2010 at 5:38 AM, Nathan Hammond
<w3.org@nathanhammond.com> wrote:
> PREAMBLE (to CSS feature request)
> I just spent the past little bit racking my brain... I believe that it
> is actually impossible to design CSS where elements earlier in the
> document tree are responsive to elements after them. With that
> realization I'm starting to think that this is an intentional design
> decision--if that's the case then all I'm looking for in response to
> this email is confirmation. Sure, I might complain a little bit (it's
> a bit limiting! :), but I can see it getting complicated to implement
> in terms of applying styles and only needing to parse the document in
> one direction.
> In any case, the use case I have is to design CSS that is responsive
> (on both sides) to the :target pseudo-class.
> Take this selector for example:
> ul > li:target + li + li
> This selects the second list item following the focused list item.
> Because the selected element is *after* :target, we can make it
> responsive to the change in :target. However, we have no way to modify
> elements preceding the :target in the document order...
> Making up a selector that doesn't work:
> ul > li:not(li:target):not(li:target~li):nth-last-child(1)
> This mythical selector that abuses existing pseudo-classes in ways
> they don't actually work would:
> 1. Grab all the list items of the unordered list,
> 2. Remove from the set the targeted list item,
> 3. Remove from the set all list items that follow the targeted list item, and
> 4. Finally select the element that appears last in the remaining set.
> The result of this magical selector would be the list item immediately
> preceding the targeted list item which could then be styled
> conditional to :target, achieving my goal.
> Thoughts? Reasons this can't be done? Things I missed entirely?

Rather than type out the reasons why it can't currently be done
myself, I'll let Jonathan Snook do the honors:

(The same reasoning that applies to parent selectors applies to
previous sibling selectors.)

I'll happily answer any additional questions you may have or provide
further clarification, of course.

Received on Thursday, 28 October 2010 14:16:54 UTC

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