xml - Why is there no prefix associated with this xmlns? -

i'm playing around xmpp , learning xml. here example of element retrieve registered users xmpp docs:

 <iq from='bard@shakespeare.lit/globe'         id='get-registered-users-num-1'         to='shakespeare.lit'         type='set'         xml:lang='en'>       <command xmlns='http://jabber.org/protocol/commands'                 action='execute'                node='http://jabber.org/protocol/admin#get-registered-users-num'/>     </iq> 

why there no prefix before xmlns namespace? why not:

<command xmlns=get_users:'http://jabber.org/protocol/commands'                 action='execute'                node='http://jabber.org/protocol/admin#get-registered-users-num'/> 

does mean it's defining namespace 1 child element <command> only? if so, why that?

this referred 'default' namespace. it, essentially, prefixes attributes (and elements) of element declared on namespace (which, in case http://jabber.org/protocol/commands), making equivalent this:

<command xmlns:default_namespace="http://jabber.org/protocol/commands"        default_namespace:action="execute"        default_namespace:node="http://jabber.org/protocol/admin#get-registered-users-num" /> 

if have children of node, have same default namespace prefixed them automatically (unless had different default namespace).

it's pretty handy if you're dealing 1 namespace, things can go out of hand rather fast if you're dealing multiples.

xpath can have issues default namespaces well, if using parse xml, beware!