See PEX Escapes for a list of PEX Escape functions and related topics.
PEXEscape and PEXEscapeWithReply are functions which provide a standard interface to functionality not defined by PEX but available in a particular PEX implementation. PEXSetEchoColor is a convenience function for easu access to the one standard PEX escape.
The PEXEscape and PEXEscapeWithReply functions each require an escape ID and a data record containing any data needed by the escape. The entity defining the escape defines the ID and the encoding of the escapes's data record and reply data record, if needed. In general, the entity defining the escape provides C language header files containing defined constants for the IDs and structure type definitions for the input and reply data records. You can use these constants and definitions directly in the escape functions' arguments. The standard place to locate these header files is <X11/PEX5/extensions>.
Before attempting to use an escape, the client program should ensure that the implementation supports the escape by checking the list of supported escapes returned by the PEXGetEnumeratedTypeInfo function.