What actions can a burrowed creature take?

A player in my upcoming game wants to play a burrowing race. I couldn’t find rules about what sort of actions a burrow creature can take.

Do rules exist for burrowing creatures:

  • Attacking from underground?
  • Getting cover underground?
  • Casting spells underground?

Note: I see this question has been answered for 4E, but this question is specifically about RAW Pathfinder.