This gem includes all schema from OfficeOpenXML-XMLSchema-Transitional.zip and OpenPackagingConventions-XMLSchema.zip as per ECMA-376, Third edition. opc schema require an internet connection to import remote schema from dublin core for dc, dcterms and xml namespaces. Those remote schema are included in this gem, and the original files have been altered to refer to the local versions.
If by chance you are able to creat a package that does not validate it indicates that the internal validation is not robust enough and needs to be improved. Please report your errors to the gem author.
Validate all parts of the package against xsd schema.