Saving macros defined on-the-fly (F3, F4)

[Van L]

> [snipped] to save a macro quickly defined using F3 and F4 
> and have it recalled at a later time and run by pressing F4 ?

(info "(Emacs)Save Keyboard Macro”) says

— quote

   To avoid problems caused by overriding existing bindings, the key
sequences ‘C-x C-k 0’ through ‘C-x C-k 9’ and ‘C-x C-k A’ through ‘C-x
C-k Z’ are reserved for your own keyboard macro bindings.

— quote ends

Before learning this, I had been binding macro to undefined keys. 
Typically, prefering the hyper and, secondly, the super modifier.