doc of prompt change with minor mode for read-key-sequence?

[Drew Adams]

I may not be characterizing this 100% correctly, but perhaps this will help
someone knowledgeable to understand.

I have this:

;; Make [pause] key be a synonym for `C-x 8' (compose key).
(define-key key-translation-map [pause]
  (lookup-key key-translation-map "\C-x8"))

I also have a minor mode named "Foo".

When I do `C-h k' without the minor mode active, and hit the [pause] key,
the prompt remains "Describe key: " (that is, I see "Describe key: pause-").
When I do the same thing with the minor mode active, the prompt changes to
"Foo: " (and there is no "pause-" to indicate the prefix).

It took me quite a while to discover where this second prompt was coming
from. Because the translation happens at a low level, I couldn't figure out
a way to debug it. By experimenting and searching source code, I found that
"Foo: " comes from the name of the minor-mode keymap: (make-sparse-keymap
"Foo"). (I don't know where the ": " is appended or in what code that takes
place.)

Questions:

1) Why does this happen? What is the purpose of the prompt change? Why
doesn't "pause-" appear, as it does without the minor mode?

2) What are users to understand by this? Should the prompt instead say at
least "Foo mode: " perhaps, to at least let users know what "Foo" refers to?

3) Shouldn't this be documented somewhere, especially since it is so
difficult to find/debug (being a low-level translation)?