VirtIO html render failure using htlatex

Hi,

I was attempting to re-build the VirtIO specifications since upgrading
my main machine to Debian Trixie. The build fails to complete with:

  ! Undefined control sequence.
  \f:HBorder ...border-top:1px solid \#\hline:color 
                                                    ;"></td>
  l.867 R
         ead / Write & Device Specific & \\
  ? 
  ! Emergency stop.
  \f:HBorder ...border-top:1px solid \#\hline:color 

The final result is an empty html file. I verified this was a regression
by running the same build on Bookworm using distrobox. It also works
with the latest Ubuntu. I confirmed it fails on the latest 
texlive image:

  📦[alex@texlive virtio-spec.git]> htlatex --version
  This is pdfTeX, Version 3.141592653-2.6-1.40.28 (TeX Live 2025) (preloaded format=latex)

I've created a minimal test case that triggers the problem:

--8<---------------cut here---------------start------------->8---
\documentclass{article}
\usepackage{hhline}
\begin{document}
\begin{tabular}{ |l||l|l| }
\hline
Bits & Device Specific & Purpose \\
\cline{1-2}
Read / Write & Device Specific & \\
\cline{1-2}
Purpose & Device Specific & \\
\hline
\end{tabular}
\end{document}
--8<---------------cut here---------------end--------------->8---

save as test.tex and run:

  htlatex test.tex

I'm aware make4ht is an alternative which fails with a slightly
different set of errors:

  📦[alex@texlive virtio-spec.git]> make4ht test.tex "html5"
  [STATUS]  make4ht: Conversion started
  [STATUS]  make4ht: Input file: test.tex
  [ERROR]   htlatex: Compilation errors in the htlatex run
  [ERROR]   htlatex: Filename     Line    Message
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.8 R ead / Write & Device Specific & \\ The control sequence at the end of the top line
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.8 R ead / Write & Device Specific & \\ The control sequence at the end of the top line
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.10 P urpose & Device Specific & \\ The control sequence at the end of the top line
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.10 P urpose & Device Specific & \\ The control sequence at the end of the top line
  [ERROR]   htlatex: Compilation errors in the htlatex run
  [ERROR]   htlatex: Filename     Line    Message
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.8 R ead / Write & Device Specific & \\ The control sequence at the end of the top line
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.8 R ead / Write & Device Specific & \\ The control sequence at the end of the top line
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.10 P urpose & Device Specific & \\ The control sequence at the end of the top line
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.10 P urpose & Device Specific & \\ The control sequence at the end of the top line
  [ERROR]   htlatex: Compilation errors in the htlatex run
  [ERROR]   htlatex: Filename     Line    Message
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.8 R ead / Write & Device Specific & \\ The control sequence at the end of the top line
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.8 R ead / Write & Device Specific & \\ The control sequence at the end of the top line
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.10 P urpose & Device Specific & \\ The control sequence at the end of the top line
  [ERROR]   htlatex: ./test.tex   ?        Undefined control sequence.
  [STATUS]  htlatex:  <- ;"></td> l.10 P urpose & Device Specific & \\ The control sequence at the end of the top line
  [STATUS]  make4ht: Conversion finished

Running the same command on Debian Bookworm yields:

  📦[alex@debian-bookworm virtio-spec.git]> make4ht test.tex "html5"
  [STATUS]  make4ht: Conversion started
  [STATUS]  make4ht: Input file: test.tex
  [STATUS]  make4ht: Conversion finished

For references the working versions are:

  📦[alex@debian-bookworm virtio-spec.git]> make4ht --version
  make4ht version v0.3l
  📦[alex@debian-bookworm virtio-spec.git]> htlatex --version
  This is pdfTeX, Version 3.141592653-2.6-1.40.24 (TeX Live 2022/Debian) (preloaded format=latex)

Any suggestions?

Thanks,

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro