Multi modification

[HansOlsson]

Closes #3474

Note that:

• I only added two of the given test-cases, since the others were for merging of modifiers and I believe that should be clear enough (otherwise we can add another PR).
• I restricted this handling it to the cases we agree on, and added examples for that well. If we don't want that restriction it would be possible to exclude those commits.

[henrikt-ma]

I abstain from reviewing the technical content, as this is an area I don't understand well enough.

[HansOlsson]

@qlambert-pro does this agree with your understanding?

[maltelenz]

@qlambert-pro does this agree with your understanding?

FYI @qlambert-pro is on extended parental leave, so don't expect an answer from him in the short term.

[eshmoylova]

I believe that is consistent with what we agreed on. I like the examples. Just a souple of suggestions to clarify the text.

[HansOlsson]

I believe that is consistent with what we agreed on. I like the examples. Just a souple of suggestions to clarify the text.

That should now be done.

[HansOlsson]

I believe that is consistent with what we agreed on. I like the examples. Just a souple of suggestions to clarify the text.

That should now be done.

@eshmoylova can you re-review to indicate if you agree with the update