Ah, I think this could be separate issue then? It was a bit buried here :)

I think we can close this issue, as the spectral font is supported.

great, thanks, installed all those files in tl.

wdyt about the general problem of no htf causing ligatures to be lost? maybe could revert to "nofonts" or something if htf not found? i kind of doubt anything like that is plausible, but wanted to get your reaction ...

hi michal - It seems there are no htf files for the spectral font family (ctan.org/pkg/spectral). maybe you can run your magic setup and make them?

as a result, the following trivial file outputs o^@line (where ^@ is a zero byte) instead of "offline", with both make4ht try.tex and htlatex try.tex <usual args>. is there some way that the defaults can not result in destroying ligatures? probably not an easy thing to figure out, but figured i could ask the question :).

\documentclass{article}
\usepackage{spectral}
\begin{document}\thispagestyle{empty}
offline
\end{document}

thanks,
karl