GNU Emacs Manual
P.5 Mouse Clicks for Menus
Mouse clicks modified with the CTRL and SHIFT keys
bring up menus.
This menu is for selecting a buffer.
The MSB ("mouse select buffer") global minor mode makes this
menu smarter and more customizable. See section N.7.3 Customizing Buffer Menus.
This menu is for specifying faces and other text properties
for editing formatted text. See section T.11 Editing Formatted Text.
This menu is mode-specific. For most modes if Menu-bar mode is on, this
menu has the same items as all the mode-specific menu-bar menus put
together. Some modes may specify a different menu for this
button.(2) If Menu-bar mode is off, this menu
contains all the items which would be present in the menu bar--not just
the mode-specific ones--so that you can access them without having to
display the menu bar.
- This menu is for specifying the frame's principal font.