For your #2, quoting from the link:
Loads and stores are relative to the X, Y, and Z registers, which are aliases for the 16 bit register pairs starting at r26, r28, and r30 respectively (r30 is an alias for Z)
Loads and stores are relative to the X, Y, and Z registers, which are aliases for the 16 bit register pairs starting at r26, r28, and r30 respectively (r30 is an alias for Z)