1282772 - document.querySelectorAll behaviour fails/succeeds in returning extant matching elements that are children of anon content depending on the selector

Status: RESOLVED DUPLICATE of bug 1282787

(Core :: DOM: Core & HTML, defect)

Description

[:Gijs (he/him)]

Here's a fun one...

STR:

0. open nightly
1. open the identity popup by clicking the identity block next to the URL, that tells you the security state of the current page.
2. open browser console (if you haven't, enable input in the normal web dev tools' options by enabling 'chrome and add-on debugging')
3. run these two expressions:

a)
document.querySelector("#identity-popup-mainView")
// this clearly shows that the element exists and has a mainview=true attribute

b)
document.querySelector("[mainview=true]")
// this returns null.

expected is that both return the same thing (either both null or both no element).

Note that after step (1), we've appended the element in question into an anon part of the panelUI.xml XBL binding, which I'm sure is relevant (it also doesn't have the 'mainview' attribute before that).

Boris, can you help explain what's going on here? It's messing with my head.