Add rights filed

cf. #21

test/data/articles/zb_preview.xml

@@ -1,5 +1,4 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<oai_zbmath_preview xmlns:zbmath="https://zbmath.org/zbmath/elements/1.0/" xmlns:oai_zbmath_preview="https://zbmath.org/OAI/2.0/oai_zbmath_preview/">
+<?xml version="1.0" encoding="UTF-8"?><oai_zbmath_preview xmlns:zbmath="https://zbmath.org/zbmath/elements/1.0/" xmlns:oai_zbmath_preview="https://zbmath.org/OAI/2.0/oai_zbmath_preview/">
     <zbmath:author>Maynard, James</zbmath:author>
     <zbmath:author_ids>
         <zbmath:author_id>maynard.james</zbmath:author_id>
@@ -134,4 +133,15 @@
             </zbmath:ref_classifications>
         </zbmath:reference>
     </zbmath:references>
+    <zbmath:rights>Content generated by zbMATH Open, such as reviews,
+        classifications, software, or author disambiguation data,
+        are distributed under CC-BY-SA 4.0. This defines the license for the
+        whole dataset, which also contains non-copyrighted bibliographic
+        metadata and reference data derived from I4OC (CC0). Note that the API
+        only provides a subset of the data in the zbMATH Open Web interface. In
+        several cases, third-party information, such as abstracts, cannot be
+        made available under a suitable license through the API. In those cases,
+        we replaced the data with the string 'zbMATH Open Web Interface contents
+        unavailable due to conflicting licenses.'
+    </zbmath:rights>
 </oai_zbmath_preview>

xslt/articles/xslt-article-transformation.xslt

@@ -150,6 +150,17 @@
         </zbmath:reference>
       </xsl:for-each>
     </zbmath:references>
+          <zbmath:rights>Content generated by zbMATH Open, such as reviews,
+        classifications, software, or author disambiguation data,
+        are distributed under CC-BY-SA 4.0. This defines the license for the
+        whole dataset, which also contains non-copyrighted bibliographic
+        metadata and reference data derived from I4OC (CC0). Note that the API
+        only provides a subset of the data in the zbMATH Open Web interface. In
+        several cases, third-party information, such as abstracts, cannot be
+        made available under a suitable license through the API. In those cases,
+        we replaced the data with the string 'zbMATH Open Web Interface contents
+        unavailable due to conflicting licenses.'
+    </zbmath:rights>
   </oai_zbmath_preview>
 </xsl:template>
 </xsl:stylesheet>