MathJax extension does not work

[Rudolf Adamkovič]

I would like to use the "\mathclap" command from the "mathtools" package in my 
Org document. In LaTeX, it works. For HTML, I visited the Org manual [1] where 
I saw the following example:

#+HTML_MATHJAX: cancel.js noErrors.js

with a comment "it loads the two MathJax extensions ‘cancel.js’ and 
‘noErrors.js’ [132]." (As a side-note, the first link in [132] points to 404.) 
Thus, I put the following into my Org file

#+HTML_MATHJAX: mathtools.js

but it seems to do nothing; the exported HTML code not even contain the word 
"mathtools".

A file that demonstrates the problem:

#+LATEX_HEADER: \usepackage{mathtools}
#+HTML_MATHJAX: mathtools.js

\begin{equation*}
\begin{aligned}
\lim_{R\to0}F_1
=\lim_{R\to0}\frac{2PR}{P+R}
=\lim_{R\to0}\frac{2\cdot0\cdot{}R}{0+R}
=\lim_{R\to0}\frac{0}{R},
=\underbrace{\lim_{R\to0}\frac{0}{1}}_{\mathclap{\text{by L'Hôpital's Rule with 
$\frac{d}{dR}R=1$}}}
=\lim_{R\to0}0
=0.
\end{aligned}
\end{equation*}

Rudy

[1] https://orgmode.org/manual/Math-formatting-in-HTML-export.html

-- 
"Logic is a science of the necessary laws of thought, without which no 
employment of the understanding and the reason takes place." -- Immanuel Kant, 
1785

Rudolf Adamkovič <salutis@me.com>
Studenohorská 25
84103 Bratislava
Slovakia

[he/him]