5. NameTest - These QNames are path steps that refer to elements in the DFDL infoset. If such an element is in a namespace, then the NameTest QName must have a prefix which is bound to the namespace. Specifically, any default namespace is not used to implicitly qualify these NameTest QNames. This behavior is consistent with XPath expression usage in XML Schema [footnote to: Definitive XML Schema (Walmsley, ISBN 0-13-065567-8)  page 390, Section 17.8, Table 17-6 says "A child element-type name which must be prefixed if it is in a namespace".] such as in the path property of the xs:selector and xs:field elements within xs:key  and xs:unique constraints, and in related XML standards such as XSLT. Note however, that this behavior is different from the way QNames are used in other places in XML and DFDL Schemas such as the ref property of an element reference, or the dfdl:ref property of a DFDL format annotation. There a QName with no prefix must always be referring to a global declaration or definition, and so is augmented with the default namespace when needed.