Textuality - Big Letters

Design Goal: Appropriate Currency

HTML Can be good, if HTML is being generated from a database. Otherwise usually very poor - as we see on the Web.
PDF Since PDF is usually used for static legacy documents (kill/cook/freeze model), and is fast to create, currency is just fine.
SGML With SGML, you are going straight from the document source - thus you are usually guaranteed near-perfect currency.
Knowledge is a text-based application.