Mac keyboards have keys labelled "control", "alt", and "⌘" (that last one looks, as it leaves my keyboard, like a four-leaf clover, is represented by U+2318, and is often called the command key or the apple key) both to the left and right of the spacebar.

The following script displays the Tk representation of these keys

 label .l
 pack .l
 bind . <KeyPress> {.l configure -text %K}

For each key in turn, the label says:

   * control == Control_L 
   * alt == Meta_L
   * ⌘ == Alt_L

Yes, really.  Where it gets utterly confusing, however, is when the keys are used (as they almost always are) as modifiers.

 label .m
 pack .m
 bind . <Command-g> {.m configure -text "command g"}
 bind . <Option-g> {.m configure -text "alt g"}
 bind . <Control-g> {.m configure -text "control g"}

As a final note, it is useful to know that the bindings are case-sensitive; in other words, <Command-g> and <Command-G> are separate bindings, the latter perhaps more easily being understood as Command and Shift and g together.

As a postscript, it is unfortunate that whilst Windows uses the Control key as a modifier for the most common operations, e.g. Ctrl-C, Ctrl-X and Ctrl-V for copy, cut and paste respectively, [MacOS X] uses the ⌘ (command) key in the same situations.  Thus it is necessary for a cross-platform application that wishes to adhere to native conventions to define platform dependent bindings.

-- Alastair Davies 2005/07/25