GNU Fortran supports a variety of features that are not
considered part of the GNU Fortran language itself, but
are representative of various dialects of Fortran that
g77 supports in whole or in part.
Any of the features listed below might be disallowed by
g77 unless some command-line option is specified.
Currently, some of the features are accepted using the
default invocation of g77, but that might change
in the future.
Note: This portion of the documentation definitely needs a lot of work!