Testing make4ht (from learnlatex)

% !TeX make4ht
\documentclass{article}
\usepackage[T1]{fontenc}
\newcommand{\diff}{\mathop{}\!d}            % For italic
% \newcommand{\diff}{\mathop{}\!\mathrm{d}} % For upright
\begin{document}
A paragraph about a larger equation
\[
\int_{-\infty}^{+\infty} e^{-x^2} \diff x
\]
\end{document}

This now works with the current learnlatex4ht,2,mathml,mathjax,svg configuration which expands all TeX macros during the conversion. It also worked with learnlatex4ht,2,mathjax,svg with a configuration that inserted the current definition of \diff at begin document inside math so MathJax saw it.

% !TeX make4ht
\documentclass[a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage{bm}

\begin{document}

$(x+\mathbf{y})(x-\mathbf{y})=x^{2}-{\mathbf{y}}^{2}$

$(x+\bm{y})(x-\bm{y}) \bm{=} x^{2}-{\bm{y}}^{2}$

$\alpha + \bm{\alpha} < \beta + \bm{\beta}$

\end{document}

A bm.4ht file added that defines \bm to be \boldsymbol, this is the recommended definition for MathJax, although a more generic bm.4ht that did not mask the system supplied one would be better.

% !TeX make4ht
\documentclass[a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage{mathtools}

\begin{document}

\[
\begin{pmatrix*}[r]
  10&11\\
   1&2\\
  -5&-6
\end{pmatrix*}
\]

\end{document}

The mathtools package is not supported by MathJax by default. The AMS had a MathJax2 extension There is discussion of updating that to MathJax3 (there is a mathjax3 branch at that GitHub) see also at Stackexchange

% !TeX make4ht
% !TEX lualatex
\documentclass[a4paper]{article}
\usepackage{unicode-math}
\setmainfont{TeX Gyre Pagella}
\setmathfont{TeX Gyre Pagella Math}

\begin{document}

One two three
\[
\log \alpha + \log \beta = \log(\alpha\beta)
\]

Unicode Math Alphanumerics
\[A + \symfrak{A}+\symbf{A}+ \symcal{A} + \symscr{A}+ \symbb{A}\]

\end{document}

a local unicode-math-hooks.4ht suppresses font loading (to match the fontspec configurig and aliases \sym... to \math...

% !TeX make4ht
% !TEX xelatex
\documentclass{article}
\usepackage{fontspec}
\setmainfont{texgyretermes-regular.otf}
\newfontfamily\cjkfont{FandolSong-Regular.otf}
\begin{document}

ABC → αβγ → {\cjkfont 你好}

\end{document}

This example now works after adding \xeuniuseblock declarations to learnlatex4ht.cfg as suggested by Michal.

% !TeX make4ht
%!TEX lualatex
\documentclass{article}

\begin{document}

$ 2\pi \approx \directlua{ tex.print(2 * math.pi) } $

\directlua{tex.print('$ 4\string\\pi \string\\approx' .. 4 * math.pi .. '$')}

\end{document}

This fails if the tex syntax mathjax configuration is used, but passes now with `mathml,mathjax` as the math is expanded by TeX.

% !TeX make4ht
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{mhchem}
\begin{document}
\ce{Hg^2+ ->[I-] HgI2 ->[I-] [Hg^{II}I4]^2-}
\end{document}

For the current mathml,mathjax configuration mhchem.4ht wraps itself in \(\) so seen my MathJax TeX input parser. For tex-mathjax configuration mhchem.4ht redefined\ce to wrap itself in \ensuremath so it is seen by MathJax which has existing mhchem support.

% !TeX make4ht
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[linguistics]{forest}
\begin{document}
\begin{forest}
[VP
  [DP\\John ]
  [V’
    [V\\sent ]
    [DP\\Mary ]
    [DP[D\\a][NP\\letter]]
  ]
]
\end{forest}
\end{document}

This now works using the svg option and Michal's svg driver

% !TeX make4ht
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{xskak}
\begin{document}
\newchessgame
\mainline{1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6}

\xskakset{moveid=2w}%
\chessboard[setfen=\xskakget{nextfen}]\\[1ex]
Position after 2.\,\xskakget{lan}

\chessboard[pgfstyle=cross,
color=blue,
setfen=\xskakget{nextfen},
getpiecelists,
markfields={\cblistP,\cblistp}]

\end{document}

A xskak.4ht is provided that almost gets this right, generating images for the xskak commands The board has an alt text that is the fen description of the board position (Ulrike tells me that chess people know what this means).

% !TeX make4ht
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{pgfplots}
\pgfplotsset{width=7cm,compat=1.17}

\begin{document}

\begin{tikzpicture}
\begin{axis}[]
      % density of Normal distribution:
      \addplot [
            red,
            domain=-3e-3:3e-3,
            samples=201,
      ]
            {exp(-x^2 / (2e-3^2)) / (1e-3 * sqrt(2*pi))};
\end{axis}
\end{tikzpicture}

\end{document}

This now works using the svg option and Michal's svg driver

% !TeX make4ht
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{musixtex}

\begin{document}

\begin{music}
\parindent10mm
\instrumentnumber{1}
% a single instrument
\setname1{Piano}
% whose name is Piano
\setstaffs1{2}
% with two staffs
\generalmeter{\meterfrac44}
% 4/4 meter chosen
\startextract
% starting real score
\Notes\ibu0f0\qb0{cge}\tbu0\qb0g|\hl j\en
\Notes\ibu0f0\qb0{cge}\tbu0\qb0g|\ql l\sk\ql n\en
\bar
\Notes\ibu0f0\qb0{dgf}|\qlp i\en
\notes\tbu0\qb0g|\ibbl1j3\qb1j\tbl1\qb1k\en
\Notes\ibu0f0\qb0{cge}\tbu0\qb0g|\hl j\en
\zendextract
% terminate excerpt
\end{music}

\end{document}

A Configuration musixtex.4ht is provided so that music environments generate an image.