built-in shelf
sgml-dtds is a built-in shelf used to store compiled SGML DTDs. These items are typically created and
used as follows:
creating with either document or subdocument) assigns an item of the shelf to be the compiled DTD. If the item did not previously exist,
it is created.
instance or with document-element) uses an
item of the sgml-dtds shelf. An item of this shelf can be used any number of times. Items can even
be used simultaneously for nested do sgml-parse actions.
Apart from this special syntactic support, the sgml-dtds shelf behaves like an ordinary shelf of type
sgml-dtd.