Support --base-header-level=-1

[rauschma]

Use case: the topmost level in my content is ##, but I’d like it to be output as if it were #.

Details: I’m finding that \parts don’t work well for EPUB and MOBI, but are nice for PDF. So my work-around is to exclude the parts for the former two. However, then the top heading level is ## and I’d like to reduce it to #. --base-header-level=-1 would be the simplest solution.

[mb21]

I’m finding that \parts don’t work well for EPUB

ePUB actually contains HTML not LaTeX, so not sure what you mean.

Also, base-header-level actually defaults to 1...