<!-- example -->
<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:enumeration value="Audi"/>
    <xs:enumeration value="Golf"/>
    <xs:enumeration value="BMW"/>
  </xs:restriction>
</xs:simpleType>

<!-- example -->
<xs:complexType name="personinfo">
  <xs:sequence>
    <xs:element name="firstname" type="xs:string"/>
    <xs:element name="lastname" type="xs:string"/>
  </xs:sequence>
</xs:complexType>

<xs:complexType name="fullpersoninfo">
  <xs:complexContent>
    <xs:extension base="personinfo">
      <xs:sequence>
        <xs:element name="address" type="xs:string"/>
        <xs:element name="city" type="xs:string"/>
        <xs:element name="country" type="xs:string"/>
      </xs:sequence>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>

<!-- example -->
<element name="callMyApp" type="dc:processingHook" />
<callMyApp/>

https://www.w3.org/TR/xmlschema-2/#built-in-datatypes
http://www.xml.com/pub/a/2001/08/22/easyschema.html -> best article
That leaves us with <complexType> with <complexContent>, which ensures that there will not be any data content in the element.

<complexType name="processingHook">
  <complexContent>
    <restriction base="xs:anyType"> -> the default syntax for complex types is complex content that restricts anyType
    </restriction>
  </complexContent>
</complexType>

<complexType name="processingHook"></complexType>

<!-- example -->
<product prodid="1345" />

<xs:element name="product">
  <xs:complexType>
    <xs:complexContent>
      <xs:restriction base="xs:anyType">
        <xs:attribute name="prodid" type="xs:positiveInteger"/>
      </xs:restriction>
    </xs:complexContent>
  </xs:complexType>
</xs:element>

<xs:complexType name="prodtype">
  <xs:attribute name="prodid" type="xs:positiveInteger"/>
</xs:complexType>

<!-- example -->

http://stackoverflow.com/questions/5457217/xsd-for-simplecontent-with-attribute-and-text
Apparently, you can't restrict simpleContent within a complexType, only extend it.

<shoesize country="france">35</shoesize>
<xs:complexType name="shoetype">
  <xs:simpleContent>
    <xs:extension base="xs:integer">
      <xs:attribute name="country" type="xs:string" />
    </xs:extension>
  </xs:simpleContent>
</xs:complexType>

<!-- example -->
<marks>95</marks>
<xs:element name="marks">
  <xs:simpleType>
    <xs:restriction base="xs:integer">
      <xs:minInclusive value="0"/>
      <xs:maxInclusive value="100"/>
    </xs:restriction>
  </xs:simpleType>
</xs:element>