How does entity mapping validation work?

[ro0NL]

Since we're migrating YAML to PHP attributes, im wondering how the validation works:

$ bin/console doctrine:schema:validate --skip-sync

Mapping
-------

                                                                                                                        
 [OK] The mapping files are correct.            

But when creating a db migration script we see:

In MappingException.php line 357:
                                                                                                                                                                                          
  Class "Some" sub class of "Other" is not a valid entity or mapped super class.
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