API IsModifiedClick

From WoWWiki

Returns 1 if the keys for the specified action are down, nil otherwise. This function replaced IsAutoLootKeyDown() and IsActionSelfCastKeyDown()

isHeld = IsModifiedClick("action")

Arguments

action 

String - The action to check for. Actions defined by Blizzard: SELFCAST, AUTOLOOTTOGGLE, STICKYCAMERA, CHATLINK, DRESSUP, SOCKETITEM, SPLITSTACK, PICKUPACTION, COMPAREITEMS, OPENALLBAGS, QUESTWATCHTOGGLE

Returns

isHeld 

1 if the modifier is being held, nil otherwise.