header idiom is used by many languages. But they don't mean the same thing , like the confusion between the web page header (visual) & the compiled languages headers.
This tag is deprecated because it lacks discriminating power. Please use a more specific tag instead, e.g.: html-heading, email-header etc.
Here in AU, it contains around 54 tagged question. All the ones I have checked were targeting C/C++ Headers.
I failed to write a usage guide (excerpt) for such generic tag