"This Style Guide for the Branch Libraries of the New York Public Library explains the markup and design requirements for all Branch Libraries web projects, along with various standards and best practices."
The rules of XHTML as compared to HTML—an easy transition
What is XML?
A brief introduction to the foundation of XHTML
Four key benefits of converting from HTML to XHTML
XHTML Authoring Tips & Tools
Simplifying the work process—includes tips on thinking structurally, and tools for hand-coders and Dreamweaver users
XHTML Accessibility Tips
Making sure your pages can be read by all visitors, browsers, and devices
Ensuring interoperability by avoiding errors and sticking to standards
Tips on authoring and linking to Style Sheets
Steal These Style Sheets!
Style Sheets for your use in Library projects
Ensuring that your Style Sheets are error-free (same as XHTML validation)