Fix document root path step (issue #46)

  - Always select the document root even if item is a child

elementpath/xpath1/_xpath1_operators.py

@@ -675,10 +675,11 @@ def select_child_path(self, context=None):
         if is_document_node(context.root):
             yield context.root
     elif len(self) == 1:
-        if is_document_node(context.root) or context.item is context.root:
-            if not isinstance(context, XPathSchemaContext):
-                context.item = None
-            yield from self[0].select(context)
+        if not isinstance(context, XPathSchemaContext):
+            context.item = None
+        else:
+            context.item = context.root
+        yield from self[0].select(context)
     else:
         items = set()
         for _ in context.inner_focus_select(self[0]):

tests/test_xpath1_parser.py

@@ -451,7 +451,9 @@ def test_node_types(self):
 
         context = XPathContext(root)
         context.item = None
-        self.check_value("/self::node()", expected=[], context=context)
+        # lxml differs: doesn't consider the document position even if select from an ElementTree
+        self.check_value("/self::node()", expected=[root], context=context)
+
         context.item = 1
         self.check_value("self::node()", expected=[], context=context)
 
@@ -1254,7 +1256,7 @@ def test_path_step_operator(self):
         self.check_value('/A', [root], context=context)
 
         context = XPathContext(root, item=root[0][0])
-        self.check_value('/A', [], context=context)
+        self.check_value('/A', [root], context=context)
 
     def test_path_step_operator_with_duplicates(self):
         root = self.etree.XML('<A>10<B a="2">11</B>10<B a="2"/>10<B>11</B></A>')