- Entities and Unicode--data representation
- XML namespaces--mixed vocabularies
- DTDs, XML schemas, RELAX NG--structural constraints and data types
- XLinks, XPointers, XPath--Linking and addressing
- CSS, XSL-FO--Presentation of XML
- Web Accessibility
<or:oranges xmlns:or="fruit://osu/or"
xmlns:ap="fruit://osu/ap" >
<ap:apples count="3" >...</ap:apples>
<cocktail or:count="5" ap:count="2" >...</cocktail>
</or:oranges>