What does the “USER” programmable key function do on the Yaesu FT-897D?

Question

I was just reviewing the manual of my Yaesu FT-897D to remind myself of useful functions I might have forgotten about, and I found the programmable function keys, which can be set to any of “All Multi Function , all Menu Item, MONI, Q.SPL, TCALL, ATC and USER” (sic).

MONI, Q.SPL, TCALL, and ATC are explained elsewhere, more or less, but what is USER?

I tried assigning it to a button and it operates as a toggle, but doesn't have any obvious effect. The only mentions of “USER” in the manual are in reference to the USER-L/USER-U digital sub-modes which seem to be independent.

Answer 1

This is from post 35317, Jan 7, 2012 in the Yahoo Group for the FT-897:

With reference to my post in December I have since had a word from Yaesu that the USER setting for menu items 65 to 70 is reserved for future use and not to be used.