In this section:
HELP_LOOKUP takes two character string arguments giving the full path name of a help file (.CHM) followed by the keyword that identifies the topic to display. The keyword must appear in the (.HHK) keyword file of the Microsoft project used to build the .CHM help file. When the main window closes, the help window will also be closed if it has been left open.
In this context the Fortran the character variable for HELP_LOOKUP and the second keyword argument must be null terminated, for example by concatenating with char(0). An alternative callback called HELPLOOKUP does not require a terminating null. It also takes a snapshot of the keyword so that, when used in a menu item, the keyword is defined at the point where the menu is created.
Keywords containing spaces must be enclosed in quotation marks. Literal strings can use double quotes within a single quoted string.