Most programming languages other than Assembly cannot not call modules that have names containing @ # or $ ( notably Fortran, which is why its run-time library has a name with a # in it so it would not conflict with any name chosen by a programmer ), so most programs, subroutines, or functions were written to use only a letter for the first character, and if the name was longer than 1 character, to use only letters and digits for the 2nd through ( up to ) 8th character . ( Note that this choice not to use # @ or $ does not apply to a " main " program written in Assembler or any language that can use these identifiers, the program loader doesn't care what the name of the module is . ) Also, modules written to be used as subroutines typically restricted themselves to 6 characters as versions of Fortran before about 1978 also can't use subroutines or modules using more than 6 characters in length.
