Here's an example of a playmode somebody might write.

If we are currently playing tune1, which, according to the
tags in the database, was on album1, by artist1 of style1,
then there is a
30% chance the next track will be the next tune on album1
20% chance it will be another tune on album1
15% chance it will be a tune on another album by artist1
10% chance it will be by another artist, of style1
and (what am I left with?)
25% chance it will be completely random

These choices could all be within the current playlist.

Richard.