Semantic Highlight Function minor mode highlights the declaration line of the current function or tag (that is to say, the first line that describes the rest of the construct).
In addition, clicking Mouse-3 on the highlighted declaration line opens a context menu that contains menu items for copying, killing, or narrowing to that tag.
The tag classes highlighted by Semantic Highlight Function
mode are the same ones given by
semantic-stickyfunc-sticky-classes. See Sticky Func
Mode.