mh-letter-toggle-header-field-display-button
mh-letter-toggle-header-field-display-button is an interactive autoloaded Lisp function in `mh-letter.el
'.
(mh-letter-toggle-header-field-display-button EVENT)
Toggle header field display at location of EVENT.
This function does the same thing as
`mh-letter-toggle-header-field-display' except that it is
callable from a mouse button.