Alison - you beat me to it! A variation (1c) is "As I came in by (obscure Irish/Scottish/English town)..."Still, I think we have overlooked one thing:
18. If the song is Irish, it should generally include a reference to whiskey.
19. If the song actually IS about drinking, well then the hero must be given a choice between: a) whiskey b) his beloved
If it is to end happily, then he chooses a).
Regards,
Henrik