php - Path types in Symfony: When to use "AppBundle:SomeEntity" or "AppBundle/Entity/SomeEntity"?

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Different Symfony docs, tutorials and howtos often use different path types to specify entities, services, etc.

For example an entity stored in src/AppBundle/Entity/SomeEntity.php can be referenced by AppBundle/Entity/SomeEntity or AppBundle:SomeEntity and $em->getRepository(**entityReference**) works with both path/reference types.

Is there a rule of thumb which type should be used when? Is there any difference or is this a matter of personal preference? Is there any manual on the path syntax used in Symfony?

BTW: I am working with Symfony 3.4. I am aware that in newer versions bundles are not used anymore. However, I think the overall questions is still the same.