Fortran '90 and later has some requirements for blanks, but a parser that also needs to be able to parse F'77 can't rely on them -- so I have to go out of the way to detect missing blanks and complain about them.

This feature makes some tokenization ambiguous without context -- is MODULEPROCEDUREFOO to be interpreted as "MODULE PROCEDUREFOO" or "MODULE PROCEDURE FOO"? But tokenization without any reserved words is a tricky problem anyway.