CSAPI is a C and C++ interface for UNIX and Windows systems. It uses Netscape Portable Runtime (NSPR), a part of the Mozilla source code that is a platform independent API to operating system services, and XPCOM for Interface Dispatch.
For documentation on NSPR see the MozillaTM technical documentation site:
For documentation on XPCOM, see:
You must use NSPR for platform-independent C data types and runtime functions in implementations that need to run on different platforms. Calendar Server uses the XPCOM C++ API (QueryInterface) to discover the exact interfaces a specific module implements.