[mediaqueries-5] Parsing strategy for range syntax

[tbjgolden]

When parsing a media query for range syntax, I was wondering about how this expression would be expected to be parsed.

(infinite = resolution)

In particular - resolution here is the feature but the parser cannot know that as it sees ident, =, ident and could match either of the top two productions in https://www.w3.org/TR/mediaqueries-5/#typedef-mf-range.

What strategy should a parser use to determine that infinite is not the feature?

A simple check for infinite on the first value? And if so, what happens with:

(infinite = infinite)

[tbjgolden]

I couldn't find any confirmation of what 'ident's might be used in a range expression, but the syntax suggests that they are valid values in a range expression - is that so and what would be an example value? I've used infinite here because it is mentioned as a valid value for resolution, presumably in a mf-plain, but I'm unsure how idents should be treated as range expression values

[tabatkins]

...huh, why are we allowing the full <mf-value> there? We should really only be allowing the three numeric types (number, dimension, ratio) in the comparison form.

Agenda+ to fix what I think is an obvious oversight here - we should change the current <mf-value> definition to:

<mf-value> = <ident> | <mf-numeric-value>
<mf-numeric-value> = <number> | <dimension> | <ratio>

and then limit the comparison syntax to only use <mf-numeric-value>.

[css-meeting-bot]

The CSS Working Group just discussed [mediaqueries-5] Parsing strategy for range syntax, and agreed to the following:

• RESOLVED: restrict comparison syntax to the mf-numeric-value production, not the mf-value production

The full IRC log of that discussion

<dael_> TabAtkins: It was pointed out that the mathematical syntax for MQs, specifically equals, <, >, etc didn't restrict the value very well. You could say resolution = infinite. You need to know too much information to know what's the MQ, what's the keyword
<dael_> TabAtkins: I think it's an oversite
<dael_> TabAtkins: prop is when you use comparision syntax we restrict value to numbers, dimensions, ratios. If you want a keyword you use colon syntax
<dael_> astearns: Opinions?
<dael_> TabAtkins: I think this is just an oversite. It's a mature spec so we need a resolution
<dael_> astearns: Prop?
<fantasai> makes sense to me
<dael_> TabAtkins: Restrict compare syntax to the mf-value production
<dael_> astearns: Objections?
<dael_> Restrict compare syntax to the mf-numeric production
<TabAtkins> restrict comparison syntax to the mf-numeric-value production, not the mf-value production
<dael_> RESOLVED: restrict comparison syntax to the mf-numeric-value production, not the mf-value production