While the native APEX refresh dynamic action restores rich text content based on the current value in the session state, the supporting dynamic action "Reset Value" refreshes rich text content to the state CLOB value when a page is loaded.
The action can be utilized to reset CLOB content on end-users' demand without refreshing a whole page. The value is always the same as long the plug-in session state is not altered using the plug-in PL/SQL API overriding onload-CLOB.
Learn more about the plug-in session state in the plug-in documentation.