Yes. This is a common situation for generic applications, such as
editors, browsers, and parsers, that are not wired to understand a
particular XML language. Such applications simply treat all element
type and attribute names as qualified names. Those names that are not
mapped to an XML namespace -- that is, unprefixed element type names in
the absence of a default XML namespace and unprefixed attribute names
-- are simply processed as one-part names, such as by using a null XML
namespace name (URI).
Note that such applications must decide how to treat documents that do
not conform to the XML namespaces recommendation. For example, what
should the application do if an element type name contains a colon
(thus implying the existence of a prefix), but there are no XML
namespace declarations in the document? The application can choose to
treat this as an error, or it can treat the document as one that does
not use XML namespaces, ignore the "error", and continue processing.