Highlight in codeblocks- extension of normal hightlight

Use case or problem

it would be useful to have highlight in codeblocks

Proposed solution

adding an extension to the event listener detecting the “=”:
when in a codeblock, having a selection, pressing “=” (once should be enough), then the selection is added to the header and the 2 equals removed and so the text highlighted.
there are 2 possibilities. doing an index inside codeblock to get the exact selection, and add for example

```js i0-5 i15-20
codeblock content indexed
```

and modifying the header when there are some overlaps… e.g adding a selection i6-18 previous selections become i0-20
and easier just highlight lines (but really less precise)

Now pressing = again on the same selection will remove the highlight and the header reference.

Current workaround (optional)

Related feature requests (optional)

or even better added to the metadata. so the user would have just the same behaviour as normal hightlight. it has to be tested if 1 or 2 = fit better