Since the message might appear several times on the same page, it's
useful to give a bit more context. Besides, usability tests show that
when there's a group with no headings, there's no clear indication on
the page that the group is actually a group and not a heading.
We're also adding some emphasis to the group name in the "Showing
headings" message, to be consistent with the emphasis we've
added the the group name in the "No headings" message.
Captions benefit blind screen reader users who navigate through tables,
particularly in this case because we potentially have several tables
with headings (one table per group), so when navigating through tables
it might be hard to know which group the headings belong to.
In this case they also benefit sighted users. Usability tests have shown
the "Groups and headings" section is a bit confusing, so adding a
caption like "Headings in Districts" helps clarifying Districts is a
group and the table refers to headings in that group.
The very same table is rendered in the "headings" step of the budget
creation wizard. However, in that case the information of the caption is
redundant because the page is specific for headings belonging to a
certain group. We're making the element invisible but still keeping it
for screen reader users in order to ease their navigation through
tables.
