Clarification of wording

[grantm]

In the aria-label and aria-labelledby section, the opening sentence says:

Sometimes we have visual elements which add information to the UI, but are missing in the UI.

I have read and re-read that several times and have failed to understand what it means. Perhaps a short example might help.

Thanks for a wonderful article by the way and apologies for accidentally submitting the issue before I'd even written the description.