Tells the application which pre-processor your plug-in needs. Most plug-ins will use one of the built-in parsers as a pre-processor to handle low level protocol issues (like bit extraction or clock polarity). Others will need full control. Plug-ins are responsible for all framing and formatting so the built-in parser options dealing with those issues are removed when used a a pre-processor.
See 'Pre-Processors' below for details