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Re: [css3-syntax] Separation of concerns: "declaration/rule-filled", "can be made important"

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Tue, 29 Jan 2013 20:49:53 -0800
Message-ID: <CAAWBYDAV4BgqBtneU_AuguOVyRWtYMEF8uJ6suM5ArUXQLgVtw@mail.gmail.com>
To: Simon Sapin <simon.sapin@kozea.fr>
Cc: www-style list <www-style@w3.org>
On Sat, Jan 26, 2013 at 10:03 AM, Simon Sapin <simon.sapin@kozea.fr> wrote:
> Hi,
> I think that CSS tokenization and tree construction should not depend on
> complex knowledge of other CSS modules. This is basic separation of of
> concerns, and our current charter also suggests that CSS syntax should be
> independent from the rest of CSS:
> http://www.w3.org/2010/09/CSSWG/charter
> I find two points in tree construction as it currently stands where this is
> not quite the case:
> 1. How to decide whether a given at-rule is "declaration-filled",
> "rule-filled" or neither.
> 2. How to decide whether a given declaration "can be made important".
> Is it guaranteed that an at-rule’s name (its at-keyword) is and will even be
> enough to decide 1.? In other words, 1. does not depend on the at-rule’s
> context/parent or its prelude.
> If this is the case, tree construction could take a list of at-rule names
> that information[1] as part of its "input", in addition to a list of tokens
> and a quirks mode flag. The introduction of §3.5. Tree Construction should
> be updated in that direction.
> [1] A mapping of at-rule names to declaration-filled/rule-filled/neither

I've now done this.  The Parser intro says that the parser must be
provided with a list of "recognized at-rules", which contains whether
the names of at-rules and whether they're rule-filled,
declaration-filled, or neither.

(Whenever the parser needs to distinguish them, the "neither" case is
always just a final "Otherwise..." clause, so unrecognized at-rules
should fall into it as well.)

> As to declarations that can be made important, I see two options:
> a. Specify that style rules contain property declarations (that can be made
> important). For at-rules, refine the "declaration-filled" concept into
> "property-filled" or "descriptor-filled". This implies that at-rules can not
> contain both property declarations and descriptor declaration, and that this
> can be decided based on the name (at-keyword) only, as above.
> b. Get rid entirely of the "can be made important" concept. Leave it to
> higher-level parsers to reject a declaration (just like `width: red` is
> rejected as invalid) if it has the important flag but can not be made
> important.
> I’m not aware of a anything in CSS that uses the style rule syntax (not
> at-rule) and contains descriptors (that can not be made important), but note
> that a. prevents using such syntax in the future.

I've done (b).

Received on Wednesday, 30 January 2013 04:50:40 UTC

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