Mixed environments

Working with and without namespaces

Namespaces aren't yet everywhere While the Namespaces in XML Recommendation is over a year old, not every XML parser supports it. Some parsers are older, some have maintainers who simply dislike namespaces, and some are minimalist tools cramming parsing into the smallest possible number of bytes. In addition, some parsers allow namespace processing to be switched off.
Avoiding collisions While the previous document illustrated a potentially dangerous situation involving namespaces, it also relies on a deliberately perverse choice of names. Where possible - most cases, in fact - keeping prefixes and URIs in a 1:1 relationship will avoid any such problems.
Most cases are simple While Namespaces in XML describes tools that accommodate all kinds of complex mixed-vocabulary situations, many documents still use only one or possibly two vocabularies. Generally, there's nothing to fear here.