The iPhone SDK provides two APIs for parsing XML. 

At the Objective C level, NSXMLParser implements an event-driven approach with a delegate object 
implementing methods for handling each of the "events" the parser encounters during its single pass over the XML data. 
Events most commonly of interest are the beginning and ending of elements and character data within elements. 

The other API in the SDK, the C library "libxml2", has a similar approach known as SAX ("Simple API for XML"). 
Because it is C, callback functions are used instead of delegate methods, 
and the parameters are C strings instead of NSString objects. 

We use the "Header Search Paths" setting for this purpose. 
The SDKROOT variable should prefix the path as the location where the SDK is installed or the SDK versions available may differ. 
For this project, the setting is:
HEADER_SEARCH_PATHS = $SDKROOT/usr/include/libxml2
