Consider whether or not to change markup for left and right pointing arrows #1368

The Required Owned Elements characteristic for certain container roles specifies that its items can be grouped.
For example, one of the Required Owned Elements for listbox is group → option.

The markup to denote this currently uses a right-pointing arrow character in an abbr element with title="containing", as follows:

<abbr title="containing" class="symbol">→</abbr>

After #1359 is merged, the Required Context Role characteristic for "groupable" item roles will also use similar markup, except with a left-pointing arrow character in an abbr with title="contained by":

<abbr title="contained by" class="symbol">←</abbr>

For example, one of the Required Context Roles for option is group ← listbox.

Unfortunately, abbr with title is problematic in screen readers. At best, the screen reader will say "right-pointing arrow" or "left-pointing arrow" (some screen readers have a setting for reading the title, but it is not the default).

This issue is to determine whether we should change this markup or leave it alone.
Random thoughts:

• if we wrap the arrow character in an aria-hidden span, do screen readers fall back to reading the title because there's no content?
• should we delete the abbr markup completely and just go with the text "containing" and "contained by"?