i submitted a gm ticket, so here's a copypaste:
"i have accidentally unbound my left mouse button(BUTTON1), now i cannot target anything in the world with my left mouse button, clicking anything in the UI works fine, just nothing in the world like mobs, npcs, players. is there any way i can restore it to its original function?"
i found out from wowwiki that the default function for right mouse (BUTTON2) is "TURNORACTION"
i assume there is a similiar name for the original function of the left mouse.