XML Namespaces: W3C Recommendation

Simple mechanism for distinguishing names from different vocabularies
Prefix in element and attribute names
Prefix bound to URI for global uniqueness
Unfortunately: does not play nice with DTDs

<az:book xmlns:az="http://www.amazon.com/namespaces/books"
         xmlns:dc="http://purl.oclc.org/dc/"
         xmlns:lc="urn:library.congress.gov:catalog"
>
  <dc:author>RK Rowling</dc:author>
  <dc:title>Harry Potter and the Goblet of Fire</dc:title>
  <az:price currency="USD">29.95</az:price>
  <az:category>children's bestsellers</az:category>
  <lc:category>PZ44.1</lc:category>
</az:book>