I CAN speak for the Newt - Ita a MIXED session . Songs AND Tunes - IF you dont want anyone to join in , SAY SO , other wise we tend to play along ! And NOT to drown out the singer !
We (Gerry and I) are there to fill gaps and maintain SOME semblance of order , so we try NOT to let one person or group take over !
Otherwise its just be polite and try NOT to start a song when someone else has just got going - There are one or two who are quieter than me !!
The Middle Bar has Twig Rule - When you are passed the twig its your turn ! And there is usually a board witha list of Fines - DONT Sing The Wild Rover is usually top of the list
Not sure how some of the other sessions run - No Doubt others will say whats what !