To create Fortran source programs, you can use any of the available text editors, such as vi or emacs. Source programs must have a suffix of .f unless the fsuffix attribute in the configuration file specifies a different suffix or the -qsuffix compiler option is used. You can also use a suffix of .F if the program contains C preprocessor (cpp) directives that must be processed before compilation begins. Source files with the .f77, .f90, or .f95 suffix are also valid.
For the Fortran source program to be a valid program, it must conform to the language definition that is specified in the XL Fortran Language Reference.