Merge branch '13-lizenzangaben' into 'master'

Resolve "Lizenzangaben"

Closes #13

See merge request !12

schema/edxml.rng

@@ -346,6 +346,7 @@
             <optional>
                 <ref name="elem.externalResources"/>
             </optional>
+            <ref name="elem.tei.availability"/>
             <ref name="elem.revisionDesc"/>
         </element>
     </define>
@@ -1479,6 +1480,18 @@
             </optional>
         </element>
     </define>
+    
+    <define name="elem.tei.availability">
+        <element name="tei:availability">
+            <ref name="elem.tei.licence"></ref>
+        </element>
+    </define>
+    
+    <define name="elem.tei.licence">
+        <element name="tei:licence">
+            <ref name="attr.tei.target"></ref>
+        </element>
+    </define>
 
     <define name="elem.tei.sic">
         <element name="tei:sic">
@@ -1645,5 +1658,9 @@
             </choice>
         </attribute>
     </define>
+    
+    <define name="attr.tei.target">
+        <attribute name="target"/>        
+    </define>
 
 </grammar>