Documentation - > Update Notification mail - > Click url - > {pre} is shown at the begining and end of that documentation heading.

Login as U1.
Edit a documentation ( created by U2 ) of a closed or open group.
Check the email of U2.
Check the Update Notification mail.
Click the url to view the changes.
http://next.dev.curriki.org/xwiki/bin/view/Documentation_Group_Closedgpmessagetest/NewDocumentationG .

It is noted that a tag,

is shown at the begining and end of that documentation heading.