Description:
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On the dirname function page of the documentation, there is a  sentence referring to the path separator character.  Actually, this should refer to the directory separator character to more closely match the PHP constant definitions of PATH_SEPARATOR and DIRECTORY_SEPARATOR.

Reproduce code:
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The current documentation:

On Windows, both slash (/) and backslash (\) are used as path separator character. In other environments, it is the forward slash (/).

Expected result:
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On Windows, both slash (/) and backslash (\) are used as directory separator character. In other environments, it is the forward slash (/).