6.1.6 Missing period in FORMAT specifications

To support legacy codes, GNU Fortran allows missing periods in format specifications if and only if -std=legacy is given on the command line. This is considered non-conforming code and is discouraged. 

REAL :: value
       READ(*,10) value
10     FORMAT ('F4')

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https://gcc.gnu.org/onlinedocs/gcc-5.4.0/gfortran/Missing-period-in-FORMAT-specifications.html