For documents with fixed markup such as forms in which the XML tags are not allowed to be
modified but only their text content, editing of the XML tag names can be disabled and
re-enabled with the 
Lock /
Unlock the XML tags action available from:
Lock /
Unlock the XML tags action available from:- The menu.
- The Source submenu from the contextual menu.
You can set the default lock state for all opened editors in the Preferences XML Editor Format preferences page.