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I would like to do something like this:
<root:secondlevel:thirdlevel
xmlns:secondlevel="http://secondlevel.com"
xmlns:secondlevel:thirdlevel="http://thirdlevel.com">
</root:secondlevel:thirdlevel>
Is there a way to do those multiple levels root:secondlevel:thirdlevel as valid XML?
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When you use multiple namespaces in an XML document, you can define one namespace as the default namespace to create a cleaner looking document. The default namespace is declared in the root element and applies to all unqualified elements in the document. Default namespaces apply to elements only, not to attributes.
When using prefixes in XML, a namespace for the prefix must be defined. The namespace can be defined by an xmlns attribute in the start tag of an element. The namespace declaration has the following syntax. xmlns:prefix="URI".
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.
No, there can be at most one namespace prefix in XML.
The XML Namespace BNF rules for names are based on QName, which allows only a single PrefixedName:
QName ::= PrefixedName | UnprefixedName PrefixedName ::= Prefix ':' LocalPart UnprefixedName ::= LocalPart Prefix ::= NCName LocalPart ::= NCName NCName ::= Name - (Char* ':' Char*) /* An XML Name, minus the ":" */
Neither Prefix nor LocalPart allow colon (:) characters, so there can be at most one colon (and at most one Prefix) part to a QName.
Side note: multiple colons are syntactically allowed in base level XML:
STag ::= '<' Name (S Attribute)* S? '>' NameStartChar ::= ":" | [A-Z] | "_" | [a-z] | [#xC0-#xD6] | [#xD8-#xF6] | [#xF8-#x2FF] | [#x370-#x37D] | [#x37F-#x1FFF] | [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF] | [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD] | [#x10000-#xEFFFF] NameChar ::= NameStartChar | "-" | "." | [0-9] | #xB7 | [#x0300-#x036F] | [#x203F-#x2040] Name ::= NameStartChar (NameChar)*
But the W3C XML Recommendation is clear that colons should not be used except for namespaces purposes:
Note:
The Namespaces in XML Recommendation [XML Names] assigns a meaning to names containing colon characters. Therefore, authors should not use the colon in XML names except for namespace purposes, but XML processors must accept the colon as a name character.
And Namespaces do not allow multiple namespace prefixes as shown above.
See also:
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