Author: Rajesh Taneja
MDL-30918 Chat: Added hidden section headers and aria attributes
http://git.moodle.org/gw?p=moodle.git;a=commit;h=02a011eabcaf740395485611d9ee0e739a1c7b46
http://github.com/moodle/moodle/commit/02a011eabcaf740395485611d9ee0e739a1c7b46
+ 2.4 en [composemessage,mod_chat]