In your code the following line
use constant kParaSpace => 4;
appears to be the setting for the gap between paragraphs when the paragraph tags are used.
When I tested your editor the gap between paragraphs is rather wider than seems to be the norm in most PerlMonks posts. Perhaps kParaSpace should be set to 2?
This is a minor nitpick; otherwise this is very slick. Kudos to you...
ScottPS: This node was written (mostly)using your editor:)