Re: documentation structure

While this style is obviously clumsier for us to compose, it does avoid relying on the user understanding what the word variadic means. Searching through online documentation of the python *args parameter, the word variadic never comes up, the closest they get is "variable length argument". I realize that python is not SQL, but I think it's a good point of reference for what concepts the average reader is likely to know.

Looking at the patch, I think it is good, though I'd consider doing some indentation for the nested <optional>s to allow the author to do more visual tag-matching. The ']'s were sufficiently visually distinct that we didn't really need or want nesting, but <optional> is just another tag to my eyes in a sea of tags.