You can view all details of api on developmentArc.
In short this api provide the solution for
1)Browser Location Utility: used to get various parts of url like servername,portnumber,protocol,fragments,query, parameters and much more.
2)Hash Table Data Structure: sequel for Flex’s arraycollection and used for large data
3)InstanceFactory: A factory class that provides the ability to create single instances at any level of scope within an application
and much more to make flex coding simple