Suggested implementation in [13ba9a50df].
For Tcl it works when adding the following CSS (example: red line around it):
<pre>
/* the format for the timeline entry with "Potential Incompatibility" */
tr.potential td.timelineTableCell {
  padding: .1em .2em;
  border: 2px solid #ff0000;
}
</pre>

Handling of multiple tags is not correct yet.