[SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] [X] [Z] x-height descriptor  XHTML  2nd      authoring tools      case sensitivity in style rule elements      deciding to use      documents in  [See XHTML documents]     DTDs          deprecated elements, and      HTML conversion software      HTML vs.      machine-generated content and      tags, quick reference      Version 1.0 and HTML 4.01      Version 1.1          elements to avoid          modules          ruby text      well-formed documents and      XML, using to define  XHTML documents     content         appearance vs.          types of      creating          DTDs, declaring          example document      ending tags in      nesting elements in  XML (Extensible Markup Language)  2nd  3rd      DTDs      as markup metalanguage      special processing directives      uses for          connecting systems          document exchange          HTML, standardizing with  xmlns attribute, defining namespaces with  <xmp> tags