Hello,
Thank you for your question.
Those class files are from other packages that are dependencies.
If you use Composer to install this package in a project, those dependency class files are loaded automatically.
If you do not use Composer, the links to the other packages are in the download package of this class package, as you may see on the page below.
Do you suggest a better place to show these package dependency classes that could be more obvious to you?
phpclasses.org/package/12853-PHP-Em
...