Transcription: there can only be one external subset and one internal subset, even when you're using modular document type definitions. The external subset is the subset that you define when you point to a file using the doctype tag. So in this case, we're pointing to a DTD that contains our element structure. Now the second DTD that we reference, we're using a parameter entity. And what it does is it literally takes the content contents of that external entity and injects it into our internal subset. So now that text and that external entity is now injected, it's now our internal subset and that gets proces ...
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