This package includes a couple of tools that you can use to automatically spell-check your SGML documents. One of the advantages of this tool over some other SGML-aware spell checkers is that it scans your documents in the form in which the SGML parser actually sees it, which means it is not line-based, system entities are resolved, marked sections are treated appropriately, etc.
Also, this tool can be made aware of particular DTDs, in the sense that it knows not to spell-check the content of elements that do not represent human-language text, such as in DocBook. An exclusion list for the DocBook DTD is included, others can be added trivially.
Home page: http://developer.postgresql.org/~petere/sgml-spell-checker/