Over a top level drop down menu this will expose the menu. If the button is held down and moved, the behavior of button 1 motion (see below) will follow.

Over an exposed menu entry this will invoke the action of the menu.

Within menu dialog boxes this will generally select a text item, and invoke a button action.

This has no effect other than that of button 1 single click.

Moving over a top level menu, or a sub-menu will cause that menu to be exposed.

If the button is released (thereby completing a click) over a menu entry that entry will be invoked.

In general button 2 click behaves as button 1 click with the menu bar.

In general button 2 double click behaves as button 1 click with the menu bar.

In general button 2 motion behaves as button 1 click with the menu bar.