Function: _def_help
Class: default
Section: default
C-Name: sd_help
Prototype:
Help:
Doc: name of the external help program to use from within \kbd{gp} when
 extended help is invoked, usually through a \kbd{??} or \kbd{???} request
 (see \secref{se:exthelp}), or \kbd{M-H} under readline (see
 \secref{se:readline}).

 The default value is the path to the \kbd{gphelp} script we install.
