I would like to add these inline extensions as additional options to Hugo’s Goldmark instances.

We have been discussing the first two ones in the Forum.

These extensions follow the same syntax as the ones for markdown-it:

• 1^st^ → 1<sup>st</sup> (see npm repo)
• H~2~O → H<sub>2</sub>O (see npm repo
• ++insert++ → <ins>insert</ins> (see npm repo

Their default configuration switch should be set to false, because every new extension adds more load to the parser and the demand is not very high.

My fork of this repo already contains the code for these extensions, including many test cases. I tried to follow the structure of the first extension passthrough and took your advice in #8 into consideration.

I already build a local Hugo version including these extensions and would know how to integrate them.