"Grant Robertson" <bogus@b...> wrote in message 
news:MPG.202dc3e4aad002db9896f8@n......
> As I am learning about XML I seen that xmlns is used with a colon after
> it as if it were a namespace itself. However, I have never seen a URI
> given for it. Is "xmlns" a sort of predefined word in that all XML
> software just knows what it means without it needing a URI?
>
> Are there any more of these special words that need no definition within
> any schema? I know there are other special words like "element" and
> "targetNamespace" but these seem to be defined within the XML Schema
> schema definition. It seems that only "xmlns" must be known before
> anything else can be known.
>
> Am I totally missing the boat on this or what?

First of all, any namespace "needs" (has) a namespace-uri. What you are 
asking here is not namespaces that don't have uri-s, but *reserved 
prefixes*, that must always be associated with specific namespace-uri-s

There are two such reserved prefixes (xml and xmlns) and they are listed in 
the Namespaces specification 
(http://www.w3.org/TR/xml-names/#sec-namespaces):

"Namespace constraint: Reserved Prefixes and Namespace Names
The prefix xml is by definition bound to the namespace name 
http://www.w3.org/XML/1998/namespace. It MAY, but need not, be declared, and 
MUST NOT be bound to any other namespace name. Other prefixes MUST NOT be 
bound to this namespace name, and it MUST NOT be declared as the default 
namespace.

The prefix xmlns is used only to declare namespace bindings and is by 
definition bound to the namespace name http://www.w3.org/2000/xmlns/. It 
MUST NOT be declared . Other prefixes MUST NOT be bound to this namespace 
name, and it MUST NOT be declared as the default namespace. Element names 
MUST NOT have the prefix xmlns.

All other prefixes beginning with the three-letter sequence x, m, l, in any 
case combination, are reserved. This means that:

  a.. users SHOULD NOT use them except as defined by later specifications

  b.. processors MUST NOT treat them as fatal errors.

Though they are not themselves reserved, it is inadvisable to use prefixed 
names whose LocalPart begins with the letters x, m, l, in any case 
combination, as these names would be reserved if used without a prefix. "

So, when using a global attribute like xml:space, one doesn't need to define 
the prefix "xml" -- it is known to the parser.



Cheers,

Dimitre Novatchev