Note: some content on this page has had aria-hidden="true" added for more precise testing.
th elements have a red outline, th[colspan] elements have a green outline.
To make sure the table still makes semantic sense (and sense for screen reader users), we double up the column headers, then visually hide one of them.
We need to be careful if we set display on a column header th. This can change its implicit role, breaking the table semantics! We would need to add role="columnheader" so that the table keeps its semantics.