What I discovered so far is as follows. There is a declaration (?) of 'sink' sink.hw0 which seems to be internal or external speaker depending on if there's headphone connected, sink.hw1 which seems to be BT headset and sink.hw0and1 which seems to be used to play on both bt headset and int/ext speaker. This is defined in /etc/pulse/system.pa
And also there's a file /etc/pulse/xpolicy.conf where several parts of signal routing policy are defined.
Example:
[device]
type = bthsp
sink = equals:sink.hw1
flags = disable_notify
This seems to be a routing policy for audio output when bt headset is connected.
But what are 'ihfandbthsp', 'ihfandheadset' and 'ihfandheadphone' devices for ? How to use them ?

Unfortunately I couldn't find any documentation related to xpolicy.conf syntax.

Any ideas or links to docs ?