In the following example, only the results of the initial invocation (in
response to the XSPEC> prompt) are given. Subsequent `XHELP` characters and
sub-topic names can be given, until control is returned to XSPEC via the <EOF>.
XSPEC> help ! Go to the top of the help file.
XSPEC> help command fit ! Go to the help text for the fit command.
XSPEC> he com he exam ! Go to the example text for the help command.
XSPEC> help model pow ! Go to the help text for the powerlaw model.