Namespaces-PHP namespace question?

{Code...} when the above two writing methods are correct in a php file without a namespace, why?

Why is the above two write methods correct in a php file without a namespace?

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Why is the above two write methods correct in a php file without a namespace?

If the namespace is not prefixed\PHP searches for the current namespace,
However, if our current environment does not have a namespace, that is, it is under the root namespace, it will naturally match with a prefix.\.

If no namespace is defined, it is global by default.