While not enforced at the language level, PSR-1 states that "Files SHOULD either declare symbols (classes, functions, constants, etc.) or cause side-effects (e.

While not enforced at the language level, PSR-1 states that "Files SHOULD either declare symbols (classes, functions, constants, etc.) or cause side-effects (e.g. generate output, change .ini settings, etc.) but SHOULD NOT do both." Basically it stipulates that you should keep classes outside of the main page loader to be compliant.