Default tag in conf.py missing
I would expect that if I call
sphinx-build -b html
tags.has('html') in conf.py would evaluate to True. The documentation (http://sphinx-doc.org/markup/misc.html#tags) makes it out like html, latex, and text are default tags for the only directive, but they don't seem to be for the tag object in conf.py.
It would be nice to know which builder was called in the conf.py file, without having to specify a tag.