How can I add htmlid to this special symbol, such as { or sqrt

[chenLe1232]

I try to perform some animation operations based on the HTML fragment rendered by Katex, but I find that I can't add htmlid to the following special characters.

eg: \begin{Bmatrix}
   a & b \\
   c & d
\end{Bmatrix}

[edemaine]

Indeed, it's difficult to add an id to a bracket made via \left.

Here's one approach to identifying the element:

\htmlId{my-matrix}{\begin{Bmatrix}
   a & b \\
   c & d
\end{Bmatrix}}

Then you can get the open bracket via document.queryElement('#my-matrix .mopen') or document.queryElement('#my-matrix > .minner > .mopen.

Another approach would be to avoid using \left, and instead use explicit sizing macros. For example, this looks approximately the same:

\htmlId{my-matrix}{\bigg\{}\!\!
\begin{array}{cc}
   a & b \\
   c & d
\end{array}
\!\!\bigg\}

Hopefully one of these works for you!

[chenLe1232]

Please forgive me. I don't know how to express my gratitude. I can only choose to donate a little money on the home page every month, hoping to help you.
Thank you for answering this question. Of course, I'm willing to pay some consulting fees.

[edemaine]

Glad I could help! No need to pay me, but thank you for supporting KaTeX!

[chenLe1232]

I was surprised to see the second method. I met this writing method for the first time. How can I learn the knowledge of similar macros? Can you recommend relevant learning resources or website? Thank you very much.

[edemaine]

One good resource is KaTeX's own documentation of supported commands: https://katex.org/docs/supported.html#delimiters

Here's one general LaTeX resource which briefly covers delimiter sizing: https://www.overleaf.com/learn/latex/Brackets_and_Parentheses