We use splitters all over the place, this bug is about creating them as an HTML custom element for use in the 3-pane and address book tabs.

Pushed by geoff@darktrojan.net:
https://hg.mozilla.org/comm-central/rev/0a6aa6aabf74
Create a splitter custom element. r=mkmelin

(In reply to Geoff Lankow (:darktrojan) from comment #0)

We use splitters all over the place, this bug is about creating them as an HTML custom element for use in the 3-pane and address book tabs.

Since you're only mentioning 3-pane and AB, what's needed to also use this in composition window?

Generally speaking, the main problem is that parent element has to be display: grid, and possibly has to be HTML (I've never tried it with a XUL element). Some other work needs to be done to set up things like remembering the size.

I see there are three splitters in the compose window. The sidebar splitter would be straightforward. The other two are children of the same element, and that might be problematic. I don't know how well that would work.

Side note: I've been doing a lot of work on upgrading the splitter that landed in this bug, and will file a new bug about it soon.

I'm planning on using this splitter in bug 1741361 (within the compose window). Are there any planned changes that I should wait for?

Also, it would be nice to make these focusable with keyboard controls and properly set aria-valuenow and aria-orientation attributes (https://www.w3.org/TR/wai-aria-1.1/#separator). I wouldn't mind doing this myself, but I don't want to step on any other changes, so please CC me.

No, I've finished everything I had planned (in bug 1744657).