1 files changed, 5 insertions, 5 deletions
diff --git a/bs4/element.py b/bs4/element.py
index 619fb73..1dd5984 100644
--- a/bs4/element.py
+++ b/bs4/element.py
@@ -148,6 +148,11 @@ class PageElement(object):
     NavigableString, Tag, etc. are all subclasses of PageElement.
     """
 
+    # In general, we can't tell just by looking at an element whether
+    # it's contained in an XML document or an HTML document. But for
+    # Tags (q.v.) we can store this information at parse time.
+    known_xml = None
+
     def setup(self, parent=None, previous_element=None, next_element=None,
               previous_sibling=None, next_sibling=None):
         """Sets up the initial relations between this element and
@@ -935,11 +940,6 @@ class NavigableString(str, PageElement):
     PREFIX = ''
     SUFFIX = ''
 
-    # We can't tell just by looking at a string whether it's contained
-    # in an XML document or an HTML document.
-
-    known_xml = None
-
     def __new__(cls, value):
         """Create a new NavigableString.