lxml compatibilit of attributes can be ensured via configuration value

DHParser/configuration.py

@@ -336,12 +336,18 @@ CONFIG_PRESET['compact_sxpr_threshold'] = 20
 # e.g. attr="<". Possible values are:
 # 'ignore' - faulty attribute values will be serialized nonetheless
 # 'fix'   - attribute values will be corrected, e.g. "<" will be
-#           replaced by the respective enity and the like
-# 'fail'  - an error will be raised. Observe that this error will be
-#           raised when serializing as XML, not when setting the value
+#           replaced by the respective entity and the like.
+# 'lxml'  - attributes values will be corrected and any non-ASCII
+#           character will be replaced by a question mark to ensure
+#           compatibility with the lxml library.
+# 'fail'  - an error will be raised, when an illegal attribute value
+#           is encountered while serializing a tree as XML. Illegal
+#           attribute values can still be set, though, since they
+#           they concern only the XMl-serialization and not the
+#           S-expression or JSON serialization.
 # Default value = "fail"
 CONFIG_PRESET['xml_attribute_error_handling'] = 'fail'
-ALLOWED_PRESET_VALUES['xml_attribute_error_handling'] = frozenset({'ignore', 'fix', 'fail'})
+ALLOWED_PRESET_VALUES['xml_attribute_error_handling'] = frozenset({'ignore', 'fix', 'lxml', 'fail'})
 
 ########################################################################
 #

DHParser/syntaxtree.py

@@ -595,7 +595,8 @@ from DHParser.error import Error, ErrorCode, ERROR, PARSER_STOPPED_BEFORE_END, \
 from DHParser.preprocess import SourceMapFunc
 from DHParser.stringview import StringView  # , real_indices
 from DHParser.toolkit import re, cython, linebreaks, line_col, JSONnull, \
-    validate_XML_attribute_value, fix_XML_attribute_value, identity, Protocol
+    validate_XML_attribute_value, fix_XML_attribute_value, lxml_XML_attribute_value, \
+    identity, Protocol
 
 
 __all__ = ('WHITESPACE_PTYPE',
@@ -1990,6 +1991,8 @@ class Node:  # (collections.abc.Sized): Base class omitted for cython-compatibil
             attr_filter = validate_XML_attribute_value
         elif attr_err_handling == 'fix':
             attr_filter = fix_XML_attribute_value
+        elif attr_err_handling == 'lxml':
+            attr_filter = lxml_XML_attribute_value
         else:
             assert attr_err_handling == 'ignore', 'Illegal value for configuration ' +\
                 'variable "xml_attribute_error_handling": ' + attr_err_handling

tests/test_syntaxtree.py

@@ -208,6 +208,22 @@ class TestParseJSON:
         assert tree.pos == 46
         assert not 'pos' in tree.attr
 
+    def test_attr_error_reporting_and_fixing(self):
+        n = Node('tag', 'content').with_attr(faulty='<&"')
+        set_config_value('xml_attribute_error_handling', 'fail')
+        try:
+            s = n.as_xml()
+            assert False, "ValueError expected"
+        except ValueError:
+            pass
+        set_config_value('xml_attribute_error_handling', 'fix')
+        assert n.as_xml() == '''<tag faulty='&lt;&amp;"'>content</tag>''', n.as_xml()
+        set_config_value('xml_attribute_error_handling', 'ignore')
+        assert n.as_xml() == '''<tag faulty='<&"'>content</tag>'''
+        n.attr['nonascii'] = 'ἱεραρχικωτάτου'
+        set_config_value('xml_attribute_error_handling', 'lxml')
+        assert n.as_xml() == '''<tag faulty='&lt;&amp;"' nonascii="??????????????">content</tag>'''
+
 
 class TestNode:
     """