idlwave-help-source-try-header

idlwave-help-source-try-header is a variable defined in `idlw-help.el'.
Its value is

t

Documentation:
Non-nil means, try to find help in routine header when displaying source.
Routines which are not documented in the system manual use their source as
help text. When this variable is non-nil, we try to find a description of
the help item in the first routine doclib header above the routine definition.
If the variable is nil, or if we cannot find/parse the header, the routine
definition is displayed instead.

You can customize this variable.