Thread:ElessarTheOnly/@comment-10507735-20180124152529/@comment-32882200-20180124175142

Not exactly, includeonly is the opposite of noinclude - everything tagged includeonly will only be relevant for the including file, but not for the template itself. This is used extensively in the template structure with separate doc file. In the doc file:

That means the template (which includes the doc file) is categorized as Template and Infobox templates, while the doc file itself is Template documentation.