The Snafu DTD defines three types of document: spaper for the production of simple technical papers, smemo for office memos and sletter for letters. They are very closely related, the main difference occuring in the treatment of the front matter (or header) of the document. The SGML construction is derived from various sources, in particular the ISO "general" document type for the base elements.
A design goal was to encourage "structure based" rather than "presentation based" markup. Formatting options are generally relegated to separate style sheets. Dependency on particular formatting systems is avoided as much as possible in the document type definitions or the external entities which they include (the TeX equation element is an obvious exception to this rule).
Only English language documents are supported. If other languages were used, it is likely that there would be problems with hyphenation, quotation marks etc. A possible extension would be the addition of an optional global attribute attached to each element allowing the language of the contents to be declared. This would allow the entry of non-English text and the use of a formatter capable of supporting multiple languages. The tag names and documentation are also English of course: the creation of non-English versions would require much more work.