Partial revert of r45109, r45116 -- removing the forced 'x' prefix from IDs not begin...

Partial revert of r45109, r45116 -- removing the forced 'x' prefix from IDs not beginning with letters.
Since we're probably going to change all our section fragments to something nicer in the next couple weeks, and nothing seems to actually explode based on what we're doing so far, I'd rather leave them be for now rather than break existing section links.