Previously, for Maya versions 2010 and below, the characters '<' and '>' would get converted to '_' if encountered in a node name or namespace name. Any leading invalid characters are removed, and all others are converted to underscore.
For example, in Maya 2009:
namespace -add "<foo>" // Result: foo_ createNode transform -n "<bar>" // Result: bar_ namespace -add "foo<bar>" //Result: foo_bar_
For Maya 2011 and above, the characters '<' and '>' will still be removed and converted to '_' for node names. However, for namespace names, Maya will consider everything in between those characters as a placeholder namespace. Therefore, you should update your code if you are using these characters and relying on Maya to correct them. For example, in Maya 2013:
namespace -add "<foo>" // Result: <foo> createNode transform -n "<bar>" // Result: bar_ namespace -add "foo<bar>" //Result: foo_bar_
After creating a reference with a namespace, never delete the namespace. All referenced objects that use this namespace are affected and will not work as expected. If you no longer want to associate a referenced object with a specific namespace, remove it using the Namespace Editor. See Remove namespaces.