All communication with the user in XSPEC is performed through the XSPEC parser, which itself sits on top of the PLT parser. The PLT parser provides a set of low level routines with a number of features such as inline editing and command recall, while the XSPEC parser handles the more complicated XSPEC-specific operations such as extraction of ranges and reprompting for failed inputs. This appendix summarizes the features of these parsers from the point of view of the user.