The long and short of adding math terms in html text is to add each term individually using the Unicode data as [&#x....;] without the square brackets. The dots represent a four digit hex number for example replacing the dots with [221A] would produce the root sign.

Useful links to Unicode data are:
https://en.wikipedia.org/wiki/Mathematical_operators_and_symbols_in_Unicode
https://www.compart.com/en/unicode/category/Sm

A clickable plugin is limited only by how many buttons you want to have for regular usage.

Ongoing Hack:
The Result and The plugin toolbar do not reflect the most recent changes.

The result
± | µ | ∑ | ° | 𝞹 | 𝝙 | ≈ | ≠ | √ | ∛ | ∜ | ∞
The vertical lines and spacing are just for clarification else: ±µ∑°𝞹𝝙≈≠≤≥√∛∜
The plugin toolbar

I have implemented it in the following way.
1. I have uploaded a folder, to [/plugins], which you can create, called [mathterms_plugin]
2. In that folder is the essential file [_mathterms.plugin.php]
3. There is an index.html, which is to stop auto access to the folder contents and
4. A css file which formats the toolbar and the buttons.

The [_mathterms.plugin.php] is a previous plugin which I have added code to make the buttons and am in the process of removing unnecessary code, so it is a bit messy from a programmer or developers view, but it works.

These are the files. They will be updated as I go along.