Q3.7.2: How do I set control/meta/etc modifiers on mouse buttons?

Use, for instance, [(meta button1)]. For example, here is a common setting for Common Lisp programmers who use the bundled ilisp package, whereby meta-button1 on a function name will find the file where the function name was defined, and put you at that location in the source file.

[Inside a function that gets called by the lisp-mode-hook and ilisp-mode-hook]

(local-set-key [(meta button1)] 'edit-definitions-lisp)