1592799 - Replace XUL-style boolean attributes with HTML-style when appropriate

Status: NEW

(Toolkit :: Themes, task, P3)

Description

[Tim Nguyen :ntim]

Currently, the XUL hidden and collapsed attributes are "XUL-style" boolean attributes, which means:

• Only a value of true hides or collapses the element in the XUL markup
• Setting el.hidden = true or any truthy value will set hidden="true" in the markup
• Setting el.hidden = false or any falsy value will remove the hidden attribute

It'd be nice to switch to "HTML-style" boolean attributes:

• Setting any value to the hidden/collapsed HTML attribute will hide the element
• Setting el.hidden = true or any truthy value will set hidden="" in the markup
• Setting el.hidden = false or any falsy value will remove the hidden attribute
• The recommended way to write things in HTML markup is <div hidden>
• The recommended way to write things in XHTML markup is <div hidden="hidden">

The current plan would be:

• Switch the current CSS to read for [hidden] rather than [hidden="true"], ditto for collapsed
• Rewrite current JS consumers of setAttribute("hidden", ...) to use .hidden = ...
• Rewrite current JS consumers of setAttribute("collapsed", ...) to use toggleAttribute or the correct values.
• As bgrins pointed out, some platform code is reading those attributes too:
  • https://searchfox.org/mozilla-central/source/dom/xul/nsXULElement.h#427
  • https://searchfox.org/mozilla-central/source/widget/cocoa/nsMenuUtilsX.mm#176
• we should be careful about XUL persistance.

Comment 1

[ExE Boss]

(In reply to Tim Nguyen :ntim from comment #0)

It'd be nice to switch to "HTML-style" boolean attributes:

• The recommended way to write things in HTML markup is <div hidden>
• The recommended way to write things in XHTML markup is <div hidden="hidden">

FWIW, I use <div hidden="true"> in my XHTML files, since the attribute’s value doesn’t matter in HTML, and XML requires all attributes to have some value. (this restriction will be lifted in XML5)

Comment 2

[Tim Nguyen :ntim]

(In reply to ExE Boss from comment #1)

(In reply to Tim Nguyen :ntim from comment #0)

It'd be nice to switch to "HTML-style" boolean attributes:

• The recommended way to write things in HTML markup is <div hidden>
• The recommended way to write things in XHTML markup is <div hidden="hidden">

FWIW, I use <div hidden="true"> in my XHTML files, since the attribute’s value doesn’t matter in HTML, and XML requires all attributes to have some value. (this restriction will be lifted in XML5)

The HTML spec explicitely says not to use true and false. It makes sense because those values are misleading: hidden=false will also hide the item. hidden=hidden or hidden="" are the recommended way on that spec.

Comment 3

[Tim Nguyen :ntim]

Gijs mentioned in https://phabricator.services.mozilla.com/D104820 that XUL attribute broadcasting will need more care:

I think for hidden this might be OK, but it's worth pointing out that XUL attribute broadcasting works differently for attribute removal vs. attributes being set to something, which can bite us if we were to do the same for disabled. In particular, the following cases:

1. button has command attribute, command gets disabled attribute (button gets it too), button's command attribute gets removed, command gets disabled attribute removed, button's command attribute is reinstated (button still has disabled attribute; the removal won't propagate)
2. button has command attribute, command gets disabled attribute set to true (button gets it too), button's command attribute gets removed, command gets disabled attribute set to false, button's command attribute is reinstated (button gets its disabled attribute set to false)