The previous GA parser, which understood only DTDL v2, allowed undefined extensions in models. The current parser supports configurable support for undefined extensions via ParsingOptions, but the presence or absence of support applies to models in all versions of DTDL, and the default behavior (with no option specified) is to disallow undefined extensions. For better backward compatibility, the parser should default to allowing undefined extensions for DTDL v2 models but continuing to disallow them for DTDL v3 models.
The previous GA parser, which understood only DTDL v2, allowed undefined extensions in models. The current parser supports configurable support for undefined extensions via ParsingOptions, but the presence or absence of support applies to models in all versions of DTDL, and the default behavior (with no option specified) is to disallow undefined extensions. For better backward compatibility, the parser should default to allowing undefined extensions for DTDL v2 models but continuing to disallow them for DTDL v3 models.