Library /sys$common/syshlp/lse$menu.hlb DECW buffer auto erase  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Enables or disables automatic erasing of placeholders for the current
  buffer.

  LSE erases the placeholder that the cursor is on when you type a
  character over that placeholder.  By default, this feature is active.