OASIS Catalogs for Fun and Profit
This tutorial about, Understanding Catalogs, A Use-Case for Catalogs, Registering Catalogs in a Project, Using the DOCTYPE Syntax Sense:X Aid, Navigating Catalogs, Building Composite Catalogs, Converting TR9401 Catalogs to OASIS XML Catalogs and more
EDIFACT Reference
The EDIFACT Reference is a free developer resource providing the most in-depth information on EDIFACT constructs and data models.
DTD Generator
Stylus Studio's DTD Generator supports the automatic generation and association of both internal and external DTDs based on XML instance documents.
EXSLT Tools
EXSLT support in Stylus Studio lets you extend XSLT 1.0 stylesheets and simplify many tasks including computing dates and times, performing mathematical computations, string manipulations and more.