Should common @when and if() functions be the same?

[dbaron]

The @when rule defines media() and supports() functions. The if() function defines supports(), media() and style() functions.

I understand (I think) that style() is only present for if() because if is in a value context, so style queries are possible, whereas @when is in a rule context. (But see container queries! Though I think those impose additional constraints which may be a good reason to keep them out of @when.)

However, I'm curious why there are differences in the definitions of the supports() and media() functions between these contexts. I'd initially expect them to be the same, although maybe there are good reasons for them to be different. (If so, it would be good to document them.) Should these functions basically be the same? Should they even have a common definition (which other types of conditions may add to in the future)?

(It's not clear to me that any of the current differences are substantive... but they're definitely defined in different ways right now.)

[Loirooriol]

For a more concrete question, @when media(width > 10em) treats em as the initial value since it has no context.
Should if(media(width > 10em): /* ... */) do the same for consistency, or should it use the context to resolve em?

[cdoublev]

@import also has its own supports().

Context	supports() argument
@import	<declaration> | <supports-condition>
@when	<declaration>
if()	<ident> : <declaration-value> | <supports-condition>

Context	media() argument
@when	<mf-plain> | <mf-boolean> | <mf-range>
if()	<media-feature> | <media-condition>

An argument "in parens" accepts almost any value, thanks to <general-enclosed>. But <declaration>, <media-feature>, <mf-*>, do not. However, <declaration> must be parsed as if it was specified in parens in @import, so @import 'foo.css' supports(garbabe); is still valid.

I thought these differences were editorial.

[AtkinsSJ]

Unifying these somehow would be nice! It'd simplify implementation, but also I think it's less confusing to authors if the same condition is valid wherever they put it.

For a more concrete question, @when media(width > 10em) treats em as the initial value since it has no context.
Should if(media(width > 10em): /* ... */) do the same for consistency, or should it use the context to resolve em?

My instinct would be no, it should be whatever em is in that context. That seems more useful I think? But it'd be worth seeing what's more intuitive to authors.

[bigandy]

if @when includes style queries in the same way that if() does then that would be very useful e.g. within @mixin context.