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[csswg-drafts] any-hover can't be used to detect mixed hover and non-hover capable pointers

From: Patrick H. Lauke via GitHub <sysbot+gh@w3.org>
Date: Tue, 27 Dec 2016 20:08:43 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-197751552-1482869320-sysbot+gh@w3.org>
patrickhlauke has just created a new issue for 
https://github.com/w3c/csswg-drafts:

== any-hover can't be used to detect mixed hover and non-hover capable
 pointers ==
A more focused successor to 
https://github.com/w3c/csswg-drafts/issues/737, only covering 
`any-hover` (as I can now rationalise better why `any-pointer` behaves
 the way it does, which I tried to more explicitly point out in #840)

`any-hover`, as currently specified, only evaluates to `none` when ALL
 detected pointing mechanisms are non-hover-capable. This currently 
makes it impossible to query specifically if some, but not all, of the
 pointing mechanisms is non-hover-capable (or conversely, to test if 
ALL detected pointing mechanisms are hover-capable)

Assuming two or more pointing devices are present, you can currently 
only test:

- at least one of the devices is hover-capable - `any-hover:hover` 
will evaluate to true (and currently, regardless of whether any of the
 other pointing devices is non-hover-capable, `any-hover:none` will be
 false)
- none of the devices is hover-capable - `any-hover:hover` will 
evaluate to false, `any-hover:none` evaluates to true

Scenarios that can't be tested (as they return the same as the "at 
least one..." scenario above):

- at least one, but /not/ all, device is non-hover-capable - 
`any-hover:hover` will evaluate to true, `any-hover:none` will 
evaluate to false
- /all/ devices are hover-capable - `any-hover:hover` will evaluate to
 true, `any-hover:none` will evaluate to false

As the UA should be able to ascertain the total number of pointing 
devices (since it needs to know this in order to properly evaluate 
`any-pointer`, presumably), it should be possible (and not require 
some special "we need to define what an input is" additional 
consideration, which was the major argument against #737) to also 
change when `any-hover:none` evaluates as follows:

- if ANY inputs are present that are non-hover capable, `any-hover: 
none` should evaluate to true
- if ANY inputs are present that are hover capable, `any-hover: hover`
 should evaluate to true
- if ALL inputs that are present are non-hover capable, `any-hover: 
none` should be true and `any-hover: hover` should be false
- if ALL inputs that are present are hover capable, `any-hover: none` 
should be false and `any-hover: hover` should be true
- if a mix of hover-capable and non-hover capable inputs is present, 
both `any-hover: none` and `any-hover: hover` should evaluate to true

Going back to the original scenarios, this would then allow to capture
 all possible states:

- at least one of the devices is hover-capable - `any-hover:hover` 
will evaluate to true (as before)
- none of the devices is hover-capable - `any-hover:hover` will 
evaluate to false, `any-hover:none` evaluates to true (as before)
- at least one, but /not/ all, device is non-hover-capable - 
`any-hover:hover` will evaluate to true, `any-hover:none` will also 
evaluate to true; this is a new capability that couldn't be tested 
before
- /all/ devices are hover-capable - `any-hover:hover` will evaluate to
 true, `any-hover:none` will evaluate to false; this is also a new 
capability that couldn't be tested before (with the change to `none`, 
this now actually gives you confidence in the `any-hover:none` to mean
 "none of the pointing devices is non-hover-capable)

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/841 using your GitHub 
account
Received on Tuesday, 27 December 2016 20:08:50 UTC

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