The title decoration code allows for indentation in
over-and-under decorations (rst-default-indent).
In my "under" decorations, however, I like to run the
decoration one space bigger than the text.
Another style I have seen is to run decorations to the
full document width, regardless of the title text. (In
this style, over-and-under titles are usually centred.)
It would be neat if rst.el had customizable options
allowing all these styles.
Suggestion: rst-right-only-indent for "under" decorations.
If rst-default-indent is nil (rather than 0), the
over-and-under deco goes to the right margin and the
text is centred. If rst-right-only-indent is nil
(rather than 0), the "under" deco goes to the right margin.