Animated image API questions

[Glenn Morris]

A couple of small questions about animated images:

1) image-animate:
"Animation occurs by destructively altering the IMAGE spec list."
What's destructive about it? AFAICS, it just increments the :index counter?

2) image-animate-timeout:
It takes COUNT as an argument, but calls image-animated-p (to get the
frame delay), which returns count, so does this mean the COUNT argument
is superfluous? (DELAY used to be an argument too but was removed.)