Add a test for issue #410 and a property to ModelVisitor

tests/validation/test_validation.py

@@ -485,6 +485,40 @@ def test_dynamic_schema_load(self):
         self.assertIn("schemaLocation declaration after namespace start",
                       str(ctx.exception))
 
+    def test_issue_410(self):
+        schema = self.schema_class(dedent("""\
+            <?xml version="1.0" encoding="UTF-8"?>
+            <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
+              <xs:element name="muclient">
+                <xs:complexType>
+                  <xs:choice minOccurs="0" maxOccurs="unbounded">
+                    <xs:element name="include"/>
+                    <xs:choice>
+                      <xs:element name="plugin"/>
+                      <xs:element name="world"/>
+                      <xs:element name="triggers"/>
+                      <xs:element name="aliases"/>
+                      <xs:element name="timers"/>
+                      <xs:element name="macros"/>
+                      <xs:element name="variables"/>
+                      <xs:element name="colours"/>
+                      <xs:element name="keypad"/>
+                      <xs:element name="printing"/>
+                    </xs:choice>
+                  </xs:choice>
+                </xs:complexType>
+              </xs:element>
+            </xs:schema>"""))
+
+        xml_data = '<muclient></muclient>'
+        self.check_validity(schema, xml_data, True)
+
+        xml_data = '<muclient><include/></muclient>'
+        self.check_validity(schema, xml_data, True)
+
+        xml_data = '<muclient><world/><include/></muclient>'
+        self.check_validity(schema, xml_data, True)
+
 
 class TestValidation11(TestValidation):
     schema_class = XMLSchema11

xmlschema/validators/models.py

@@ -12,6 +12,7 @@
 plus a set of functions for manipulating encoded content.
 """
 from collections import defaultdict, deque, Counter
+from copy import copy
 from operator import attrgetter
 from typing import Any, Dict, Iterable, Iterator, List, \
     MutableMapping, MutableSequence, Optional, Tuple, Union
@@ -206,6 +207,16 @@ def __init__(self, root: ModelGroupType) -> None:
     def __repr__(self) -> str:
         return '%s(root=%r)' % (self.__class__.__name__, self.root)
 
+    def __copy__(self) -> 'ModelVisitor':
+        model: 'ModelVisitor' = object.__new__(self.__class__)
+
+        for cls in self.__class__.__mro__:
+            if hasattr(cls, '__slots__'):
+                for attr in cls.__slots__:
+                    setattr(model, attr, copy(getattr(self, attr)))
+
+        return model
+
     def clear(self) -> None:
         del self._groups[:]
         self.occurs.clear()
@@ -240,9 +251,19 @@ def restart(self) -> None:
         self._start()
 
     def stop(self) -> Iterator[AdvanceYieldedType]:
+        """Stop the model and returns the errors, if any."""
         while self.element is not None:
             yield from self.advance()
 
+    @property
+    def stoppable(self) -> bool:
+        """Returns `True` if the model is stoppable from the current status without errors."""
+        model = copy(self)
+        for _ in model.stop():
+            return False
+        else:
+            return True
+
     def iter_group(self) -> Iterator[ModelParticleType]:
         """Returns an iterator for the current model group."""
         if self.group.model == 'all':