To support legacy codes, GNU Fortran permits the count field of the X
edit descriptor in FORMAT
statements to be omitted. When omitted, the count is implicitly assumed to be one.
PRINT 10, 2, 3 10 FORMAT (I1, X, I1)
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https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gfortran/X-format-descriptor-without-count-field.html