Cannot associate review comments with highlighted fragments of code

Gerrit has a really nice feature where you can select a fragment of code with which to associate your review comment.

In contrast, GitLab only allows you to associate your comment with (the whole of) a single line. This means:

• you can't clearly comment on a fragment of a line, which would be especially useful if you want to comment separately on multiple fragments within a line, and
• you can't comment on multiple lines. (UPDATE: this one is no longer true)

Proposal

Copy Gerrit's behaviour.

Links / references

GitHub has the same feature gap, so this is another opportunity to be better than GitHub :-)