730280 - API to list matching rules with their specificity

Status: RESOLVED FIXED

(Core :: DOM: CSS Object Model, defect)

Description

[Mike Ratcliffe [:miker] [:mratcliffe] [:mikeratcliffe]]

In the developer tools style tools (specifically the style doctor, rule and calculated views) we need access to the specificity of each CSSSelector. In the style doctor the displayed value could help users to diagnose why a selector is not applied to an element, in the other tools we use it to decide in which order we display the rules.

In order to achieve this we need an API. I would suggest that nsIDOMCSSRule exposes the specificities with which the rules are matched (since there it is unique). Of course, we don't currently have that information ... though we do need it for bug 561154.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Er...  nsIDOMCSSRule doesn't have a unique specificity, so I'm not sure I understand the second paragraph of comment 0.

Comment 2

[Mike Ratcliffe [:miker] [:mratcliffe] [:mikeratcliffe]]

Hmm ... I see, even cssStyleRule.cssText can contain multiple selectors so there is no place that the specificity for a particular selector could be exposed.

Comment 3

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

It could be exposed in an API that says which rules matched, since when a rule matches it's a particular selector that's matching, with a particular specificity.

Comment 4

[Mike Ratcliffe [:miker] [:mratcliffe] [:mikeratcliffe]]

That could work, something like domRules.getCSSSelectors(aRule).

Comment 6

[Mike Ratcliffe [:miker] [:mratcliffe] [:mikeratcliffe]]

This is fixed as part of another bug