Constraint "QName resolution (Schema Document)", bullet 4 states:

"4 its namespace name is either the target namespace of the schema document 
containing the QName or that schema document contains an <import> element 
information item the actual value of whose namespace [attribute] is identical 
to that namespace name." 
Does this mean that

<schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="myNS">
  <element name="e" type="string"/>
</schema>
is invalid? (Because the schema namespace is neither the target namespace, nor 
imported by this document.)

The spec does mention:

"Simple type definitions for all the built-in primitive datatypes, namely 
string, boolean, float, double, number, dateTime, duration, time, date, gMonth, 
gMonthDay, gDay, gYear, gYearMonth, hexBinary, base64Binary, anyURI (see the 
Primitive Datatypes section of [XML Schemas: Datatypes]), as well as for the 
simple and complex ur-type definitions (as previously described), are present 
by definition in every schema. All are in the XML Schema {target namespace} 
(namespace name http://www.w3.org/2001/XMLSchema ), have an atomic {variety} 
with an empty {facets} and the simple ur-type definition as their base type 
definition and themselves as {primitive type definition}. 
Similarly, simple type definitions for all the built-in derived datatypes (see 
the Derived Datatypes section of [XML Schemas: Datatypes]) are present by 
definition in every schema, with properties as specified in [XML Schemas: 
Datatypes] and as represented in XML in Schema for Schemas (normative)."

But I don't think "are present" directly leads to "can be accessed". Shouldn't 
bullet 4 of "QName resolution (Schema Document)" be changed to something like:

"4 one of the following must be true: 
4.1 all of the following must be true: 
4.1.1 its namespace name is identical to http://www.w3.org/2001/XMLSchema . 
4.1.2 the kind specified is simple or complex type definition. 
4.1.3 its local name is identical to the name of one of the built-in types. 
4.2 either the target namespace of the schema document containing the QName or 
that schema document contains an <import> element information item the actual 
value of whose namespace [attribute] is identical to that namespace name." 

See: http://lists.w3.org/Archives/Public/www-xml-schema-
comments/2002JanMar/0459.html