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Re: Marking style properties as "required" + groups of styles

From: Andrew Fedoniouk <news@terrainformatica.com>
Date: Tue, 21 Dec 2004 18:27:23 -0800
Message-ID: <003101c4e7cd$c5b9da20$bd02000a@ANDREWF>
To: "Ben Ward" <benmward@gmail.com>, <www-style@w3.org>

Hi, Ben,

I think that yours idea

| foo {
|  background-color: #F00;
|  vertical-align: bottom !required;
| }

is just perfect.

About groups.... well... probably

@if-supported opacity, ....  { }

whould be better? I am not sure though. At least it is closer to existing 
@media notation

Andrew Fedoniouk.

----- Original Message ----- 
From: "Ben Ward" <benmward@gmail.com>
To: <www-style@w3.org>
Sent: Tuesday, December 21, 2004 4:42 PM
Subject: Marking style properties as "required" + groups of styles

| Hi there, I've got something for the CSS3 'ideas' pile.
| I've recently developed a site in which the lower levels of navigation
| (lists) are hidden until a parent (a <li>) is :hover'd over. The
| effect (commonly called "Pure CSS Menus") is nice. A degraded, CSS1
| supporting version is provided in the same stylesheet by using
| CSS2 selectors (namely ">") to hide the newer content from old
| browsers. However, when testing using Konquorer 3.1.4 (the latest
| version you can get running on Windows+Cygwin, not actually the
| current version at all) I discovered a problem.
| This version of KHTML supports the ">" selector, so applied the
| collapsed menu styles, but didn't support :hover on all elements.
| Thus, the menus displayed collapsed, but the UA was unable to show
| the content when hovering.
| The CSS spec does not require UAs to only implement complete specs
| (else we'd still be without CSS1...) but when support of the same
| level of CSS varies in a UA, I would like to avoid resorting to any
| kind of JavaScript sniffing to more finely control implementation. It
| extends development time in terms of otherwise unnecessary research
| and adds to the workload of maintenance over a period of years for the
| site's lifespan.
| Hence, this proposal, (which comes in two parts).
| 1) Introduction of a "!required" declaration. This would be added to the
| CSS syntax in the same way as the "!important" declaration is used at
| the moment. It could be specified on a property-by-property basis, or
| to entire styles.
| e.g.
| foo {
|  background-color: #F00;
|  vertical-align: bottom !required;
| }
| In the above style, for a user-agent to apply the style it must
| support all properties marked as required. If a UA does not support
| 'vertical-align' (as in this example) then it should not apply
| background-color either.
| Conversely, if it did not support background-color but did support
| vertical-align, then the style should be applied with the property not
| marked as required unrendered.
| A larger example:
| foo.watermark {
|  display: none;
| }
| foo.watermark {
|  display: block;
|  position: absolute;
|  bottom: 0;
|  right: 0;
|  opacity: 10% !required;
| }
| In this case, we have an element foo (which lets say is an image that
| the author wants used as an overlaying watermark on their site).
| However, if the UA doesn't support CSS3 opacity, then the watermark
| will obscure the content of the page and make it unusable.
| The first style hides it completely from all UAs, and the second
| should only be implemented by a UA that understands 'opacity'. Thus,
| the author has no worries about his content being obscured by
| presentation.
| Part 2) A way of declaring 'groups' of styles and requiring entire
| styles within a group. In my original use case, the problem arose from
| an unimplemented :hover style. However, this was a different style
| altogether from that which was responsible for transforming the menu
| into its initial, collapsed state. It's that collapsing rule that
| needs to be ignored if :hover is not implemented, not the :hover rule
| itself (or any property within it).
| I have a less solid idea about how to declare this syntax, so consider
| this as a starting point only.
| /* a group of styles */
| @group {
|  /* the first style in the @group */
|  foo bar {
|    display: none
|    background-color: #0F0;
|    color: #000;
|  }
|  /* the second style in the @group - this is required */
|  foo:hover bar !required  {
|    display: block;
|    position: absolute;
|    top: 0px;
|    left: 1em;
|  }
| }
| ...
| In this example, a child element will only be displayed if its parent
| is hovered over. However, the :hover rule is marked as required.
| Should the UA not understand the :hover rule (or if that rule fails as
| a result of any contained property that is also marked as required)
| then everything within the @group should be ignored (therefore "bar"
| will not be hidden, and some other styles elsewhere can specify a
| degraded presentation).
| For my own use-case: The CSS for displaying the lists as popup menus
| would be wrapped within a @group { } and failure on a "li:hover"
| rule would also fail everything related to the collapsed menu system and 
| make the content inaccessible.
| N.B.
| a) If a style is marked as !required and is not contained within a
| @group, then the entire stylesheet should fail and be ignored.
| b) If a style is marked as !required, and contains a property that is
| marked as !required which then fails, then the entire style should
| fail.
| This !required syntax would allow a user-agent to perform a 'self
| assessment' on what to apply, rather than any grotesque system of
| conditional styles based on User-Agent names/Ids (c.f. Microsoft's
| conditional comments extension to HTML).
| I see no reason why !required could not also be applied to a @group
| (@group !required { }) and have the same failure inheritance applied to
| it as any other property & style relationship.
| Whether nesting @groups would be taking the idea too far away from
| interests in simpler syntax I'm less sure.
| Feedback is greatly appreciated. Kind Regards,
| Ben Ward
| -- http://www.ben-ward.co.uk
Received on Wednesday, 22 December 2004 02:27:27 GMT

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