By definition, in FORTRAN and RATFOR, a keyword is one of the
parameters such as IOSTAT used in the parameter list of an I/O
statement. For example,
open(21, FILE=file_name, STATUS='old', IOSTAT=io_flag)
Such keywords are typeset in typewriter type to better highlight them.
In FORTRAN, these keywords are case-insensitive. However,
note that certain of the lower-case forms—in particular, ‘end’,
‘read’, and ‘write’—have other special meanings, and one can
in principle use any of these keywords as ordinary variables in other parts of
the code; however, FWEB identifiers can have just one meaning
throughout the code. By default, the lower-case forms are also
recognized as keywords (except for the three special identifiers just
mentioned), so one shouldn’t use those as regular variables. To cause
only the upper-case forms to be recognized, use the ‘-k’ option.