Wikipedia:Manual of Style/Accessibility/Data tables tutorial
Providing abbreviations for long headers
Voice browsers might read aloud this data table in the following order:[1]
Caption: [caption text]
[column header 1]: [row header 1], [column header 2]: [cell 1,2], [column header 3]: [cell 1,3]
[column header 1]: [row header 2], [column header 2]: [cell 2,2], [column header 3]: [cell 2,3]
...
Note that each column header is repeated when reading every row, so an abbreviation could be added to long headers using the abbr="..." attribute[2], for example:
{|
|+ [caption text]
|-
! scope="col" abbr="Wikipedian" | Wikipedia editor
! scope="col" abbr="Edits" | Number of edits
! scope="col" | Last edit
! scope="col" abbr="Donations" | Donations (US$)
|-
...
In this example all column headers have an abbreviation except the column with the date of the last edit, which is short enough.
Row or column headers should not use colspan/rowspan to span several rows or columns – unless sub-headers are provided. Tables should not contain more than two levels of headers (which means 1) headers 2) sub-headers; but no 3) sub-sub headers).
Images or colors inside a table should meet the requirements for images and color.