An XML file whose top-level element is <library>. The two legal subelements are <path> and <component>. Each IP Index File indexes a collection of available SOP Builder components. The IP Index Files then facilitate faster startup for SOPC Builder and other tools because fewer files need to be read and analyzed. The SOPC Builder component search path searches some directories recursively, while others are only searched to a specific depth. In the following list of search locations, a recursive descent is annotated by **. The * signifies any file. When a directory is recursively searched, the search stops at any directory containing either a Component Description File (hw.tcl)or an IP Index File; subdirectories are not searched.