ng all of the entries, in the same
     manner as the History library's 'clear_history()' function.  This
     differs from 'clear_history' because it frees private data Readline
     saves in the history list.

 -- Function: void rl_activate_mark (void)
     Enable an _active_ mark.  When this is enabled, the text between
     point and mark (the REGION) is displayed in the terminal's standout
     mode (a FACE).  This is called by various Readline functions that
     set the mark and insert text, and is available for applications to
     call.

 -- Function: void rl_deactivate_mark (void)
     Turn off the active mark.

 -- Function: void rl_keep_mark_active (void)
     Indicate that the mark should remain active when the current
     Readline function completes and after redisplay occurs.  In most
     cases, the mark remains active for only the duration of a single
     bindable Readline function.

 -- Function: int rl_mark_active_p (void)
     Return a non-zero value if the mark is currently active; zero
     otherwise.