xsd - Declaring an attribute for a different namespace in XML Schema -

i've been using xml format mix of different existing formats , custom elements , attributes, , thought should write schema custom bits.

one thing use custom attributes on elements in existing formats, this:

<ns1:something atta="b" attb="a" ns2:extraatt="c"/> 

i understand doing allowed cannot think how declare "extraatt" in xml schema or, worse, in dtd.

i have tried reading specification, written in chinese far concerned. tutorials talk "name", "type", , "use", e.g. this one , that one.

each schema document defines components (pieces of schema) 1 namespace. define attribute ns2:extraatt want schema document one:

<xs:schema xmlns:xs="http://www.w3.org/2001/xmlschema"   targetnamespace="http://example.com/my-ns2">   <xs:attribute name="extraatt" type="xs:anysimpletype"/> </xs:schema> 

the declaration of element ns1:something need allow attribute somehow, either attribute reference (<xs:attribute ref="ns2:extraatt"/>) or attribute wildcard (<xs:anyattribute namespace="http://example.com/my-ns2"/> or similar).

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sorry legibility of spec; it's long story, members of wg did not think people exist ("no 1 except implementors reads spec, , long don't complain it's readable enough" -- @ least, said before implementors did complain, loudly , bitterly; changed subject).