Fortran up to 77 (well, technically still everything in fixed-form, a.k.a. punch...

Fortran up to 77 (well, technically still everything in fixed-form, a.k.a. punch-card-style source files) ignores spaces. And AFAIK there still exist both versions of e.g. "goto": "go to" and "goto" are both valid Fortran 90 and later.

This, and the fact that variable names are allowed to be implicitly defined, lead to the famous bug:

   DO 10 I = 1.100

declared the variable `DO10I` with a value of 1.1, instead of the loop from 1 to 100 and declaring the "statement label" 10:

       DO 10 I = 1,100
          SUM = SUM + I
    10 CONTINUE