Steps to reproduce

1. Enable wikitext syntax highlighting
2. Open Wikipedia:Sandbox
3. Edit as source
4. Type:

{| class="wikitable"
|+ class="z" | Z
! class="a" | A !! class="b" | B
|-
! class="c" | C || class="d" | D
|-
| class="e" | E || class="f" | F
|}

Actual results

The pipe separating the attribute and content is missing its highlight for captions, or cells beginning with double marks (|| or !!) that are not the first cell on the line.

Expected results

The pipe separating attribute and content should be highlighted for captions, or cells beginning with double mark that are not the first cell on the line.

Screenshot