Is xmlns=“” a valid xml namespace?

Question

Is \"empty\" a valid value for XML namespace? If yes what does it mean?

I have the following XML code but I\'m not sure to which namespace Field1 and

Answer 1

It is not a valid XML NS. It is not a valid XML NS declaration. Please check section 2.2 of Namespaces in XML 1.0 :

The empty string, though it is a legal URI reference, cannot be used as a namespace name.

It is however the only way to undeclare a default NS declaration if there is one in effect, or it has no effect. See. Namespaces in XML 1.0 and 1.1, section 6.2. However the 1.1 NS rec added a way to also undeclare a NS declaration with a prefix.

Thus it is valid, but it is not "a valid XML namespace" like the OP wrote it.

Answer 2

Yes, it is valid. Section 6.2 in the Namespaces in XML 1.0 Recommendation specifically says:

The attribute value in a default namespace declaration MAY be empty. This has the same effect, within the scope of the declaration, of there being no default namespace.

Quoted from comment:

It is legal, and this is the way to bring an element into the global namespace.