This button allows the user to redefine a function. Since the last "Button" of Key: in "Property Sheets->[Key]]" handles this, the left Function: can be selected and the function defined.
Note that the user can also redefine functions on the other 5 buttons (User1,...,User5) adjacent to this button. There are 6 buttons in Tool Bar on which the user can redefine functions.
[Save] can be used to register in the Registry, "-key:" can be added to [Auto Load] in [REGISTRY], and then the settings can become the defaults by using [Save] in [REGISTRY] (cf. Q_S1).