Thanks to Michal and Karl for your replies. Further investigation shows that this is a bad interaction between the bookmark driver file bkm-dvips.def and dvipng, which I can provoke without involving TeX4ht at all. I will report this to the maintainers of bookmark and dvipng, as Karl suggests.
I am already moving to using MathJax to handle maths output and experimenting with using SVG for diagrams, as Michal suggests. This will avoid any issues with dvipng, but I wanted to investigate this bug first. In the short term, using the previous version of bkm-dvips.def provides a workaround, but I will try Michal's suggestion, which may be more portable. Best wishes, Francis -----Original Message----- From: Karl Berry <[email protected]> Sent: Friday, 12 March 2021 9:34 pm To: [email protected]; [email protected] Subject: Re: [tex4ht] Bad interaction with bookmark.sty Regardless of the input, it is a bad bug in dvipng. Programs should not crash. If it is possible for someone to send me the dvi file, I could send it to the maintainer. (Or feel free to send it directly :) I won't have a chance myself to extract the dvi file that's being fed to dvipng for a while, at best. --thanks, karl.
