Sed on blocks of text

A devops guy just asked me whether sed can work on blocks of text as opposed to just lines.  Sure it can.  Try this for fun:

man man | sed -rn '/^ *-/{h;:a;n;/^ *$/{bb};s/^ *//g;H;ba;:b;x;s/^ *//g;s/\n/ /g;p}'

Happy to explain how it works.  Please note that Mac's sed is broken; please use gsed instead!