lxml compatibilit of attributes can be ensured via configuration value

DHParser/syntaxtree.py

@@ -2014,7 +2014,7 @@ class Node:  # (collections.abc.Sized): Base class omitted for cython-compatibil
                 # txt.append(' err="%s"' % (
                 #     ''.join(str(err).replace('"', "'").replace('&', '&amp;').replace('<', '&lt;')
                 #             for err in root.node_errors(node))))
-                txt.append(' err=' + (attr_filter(''.join(str(err)) for err in root.node_errors(node))))
+                txt.append(' err=' + attr_filter(''.join(str(err) for err in root.node_errors(node))))
             if node.tag_name in empty_tags:
                 assert not node.result, ("Node %s with content %s is not an empty element!" %
                                          (node.tag_name, str(node)))