alt() - unknown function?

Hi all, I've just started looking at the code of an e-commerce site we are taking over the development of, that another company has previously developed . Coupled with the difficulty of taking over development of someone else's code (also poorly commented), I've been stumped by a fatal error on a function call alt() which is dotted everywhere in the main templating script (sample below): // Get/Set a specific property of a page function getPageProp($prop,$id="") { return $this->PAGES[alt($id,$this->getPageID())][$prop]; } function setPageProp($prop,$val,$id="") { $this->PAGES[alt($id,$this->getPageID())][$prop]=$val; } It looks to be defining properties for a list of pages, with each page providing its own PageID. I've never seen this function before, nor can I find any definition of it in the site code, I was wondering if anyone recognises this, is it from a thirdparty templating tool at all? Thanks -Tom