Use of HTML in the title area appears unused (based on cursory scan of `go/sourcegraph`).
It seems that if HTML controls in the header are desired, they should be placed within the "action" section of the header, not as part of the title itself.
Let's deprecate dialog2 `titleContent` in 9.x, remove in 10. If the soy template is documented, direct users to use the action content instead of titleContent.
Usage described in documentation
Demonstration of all states
Interactive state (screen readers)
Visual regression tests
Navigation (only keyboard / only mouse)
Component render legibly
Element status (At Rest/Pressed/Selected/Read Only/Disabled)