What is the documented behaviour for use of passthrough = yes ?
The manual says: when passthrough = yes = IGNORE THIS RULE AND GO TO NEXT ONE (useful for statistics).
So assuming that we configure an action on a Mangle Rule Action of say:
Action = Mark Packet
and
New Packet Mark = FOO
and
Say that Passthrough = Yes is SET
What happens to the Action … does it get performed ?
i.e.
Is the packet going to be marked with New Packet Mark = FOO ?
F.
The action gets performed, but the next rule(s) also get evaluated instead of bailing out on the first hit
Where does it say it gets ignored? Link?
You’re confusing ‘passthrough=yes’ and ‘action=passthrough’. The latter’s documentation states “ignore this rule and go to next one (useful for statistics).”
As fewi stated, ‘passthrough=yes’ under an ‘/ip firewall mangle’ makes the rule perform it’s specified ‘action=’ and continue processing the next rule in chain. If ‘passthrough’ was set to ‘no’ then the rule would perform the specified ‘action’, and stop processing further rules in the chain.
I believe the only time ‘action=passthrough’ is not strictly used for statistics is in ‘/routing filter’ where it is used to continue processing further rules just like ‘passthrough=yes’. 
You are right. I was reading this off of the documentation, documenting the Action = Passthrough as opposed to some other action with the capability to NOT set the passthrough = CONTINUE GOING DOWN THE LIST = Yes to NO = STOP HERE.
Very much confusing but logical.
F.