Some values are not available for xset's auto-repeat rate?

For example, here is what happened when I ran xset r rate 300 100 ; xset q

xset

That looks okay. But when I replace 100 with, let’s say 101 for the repeat rate, the reported value jumps straight to 111.

xset2

My intuition tells me that some kind of hardware limitation is causing this, but I need someone to help me confirm this.

What about the long string “00fffff…” under the “auto repeating keys” section? What does that mean?