This feature is not required for SCORM 2004 compliance but it may solves many problems during manifest parsing.
A SCORM manifest is based on several XML schemas linked in the manifest, and sometimes included in the package.
I didn't find a PHP function to do this with several schemas so the solution seems to be write an XML Validator in PHP.
I search for how the others PHP LMS do this without fortune because the one that do this uses a java class called as an external command. This means that we must have a java virtual machine on the server that is not an easy thing for hosted solutions.
In a old SCORM module release I introduced a validation script written from a student (he does it as his thesys) but it validate only SCORM 2004 and with standard schemas.
I think this not may be useful in a general validation problem solution, it uses a lot of "case" and "if" to check all the CAM (Content Aggregation Model).