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# If there exists something (reasonable) that can run it, it's valid.

This includes obscure, non-standards-compliant compilers (though this should be specified in the answer if needed). So any posted program on a standard code-golf question must actually be executable and should (at least theoretically) complete the required task.

Depending on the situation, it may or may not make sense to count the compiler/interpreter flags in the byte count of the answer. The specifics depend on the language (e.g. no need to count file name or a generic "please compile" flag, but `-Dm=main(){puts("Hello, World!");}` must be counted for a C compiler.)

(The "reasonable" requirement is there to prevent needing a CPU with a specific name, precise free disk space, or just a plain file with some source code already on the file system)