Clarify Modifier doc for name and default value

[daanzu]

[daanzu]

I guess it could be handy sometimes to set a name, but it's awfully convenient to let it just take over its child's name.

[drmfinlay]

Yes, the handy default behaviour should stay. Ditto for the value of Modifier elements. I guess a different name would only make sense if the child element/extra is used more than once.

[daanzu]

Upon reflection, adding a name parameter would also be good for avoiding resulting in an error if someone passes name out of habit.