188.8.131.52 Core elements for Transcriptional Work refers to several elements as "described in section 3.4 Simple Editorial Changes" and lists them. Two of them, <abbr> and <expan>, however, are not described in 3.4. They are described in 3.5.5 Abbreviations and Their Expansions.
But it looks like what is 3.5.5 should be under 3.4.
But the title of 3.5 does include "Abbreviations." If that is right, then the text in 184.108.40.206 should say be expanded to "described in 3.4 . . . and 3.5 . . . ."
The pointer on the reference pages for <abbr> and <expan> do point to 3.5.
Maybe it's just 220.127.116.11 that is wrong.