Documentation of multirule rewriting

[amahboubi]

Hi,
I would like to improve the documentation of multirule rewriting in the manual. For the time being, the grammar describing r-items is slightly incomplete: it does not reflect the fact that their can be nested parentheses inside a list of rules, and it does not mention the "reverse switch" =^~. Yet for the moment I did not find a way to make the grammar more correct without making it at the same time a bit heavier. Any suggestion?