<schemalist> <schema id='a'> <key name='foo' type='s'> <default>''</default> </key> </schema> <schema id='b' extends='a'> <key name='bar' type='s'> <default>''</default> </key> </schema> <schema id='c' extends='b'> <key name='foo' type='s'/> </schema> </schemalist>