diff --git a/Doc/library/xml.etree.elementtree.rst b/Doc/library/xml.etree.elementtree.rst
--- a/Doc/library/xml.etree.elementtree.rst
+++ b/Doc/library/xml.etree.elementtree.rst
@@ -106,6 +106,18 @@
    '2008'
 
 
+.. note::
+
+   Not all elements of the XML input will end up as elements of the
+   parsed tree. Currently, this module skips over any XML comments,
+   processing instructions, and document type declarations in the
+   input. Processing instructions and comments can nevertheless be
+   represented as tree elements, and are included when generating XML
+   output. A document type declaration may be accessed by passing a
+   custom :class:`TreeBuilder` instance to the :class:`XMLParser`
+   constructor.
+
+
 .. _elementtree-pull-parsing:
 
 Pull API for non-blocking parsing
@@ -381,6 +393,12 @@
    string containing the comment string.  Returns an element instance
    representing a comment.
 
+   Note that the element tree XML parser skips over comments in the
+   input instead of creating comment objects for them. An element tree
+   will thus only contain comment nodes if they have been inserted
+   into to the tree using :meth:`~Element.insert`,
+   :meth:`~Element.append` or :meth:`~Element.extend`.
+
 
 .. function:: dump(elem)
 
@@ -461,6 +479,13 @@
    containing the PI target.  *text* is a string containing the PI contents, if
    given.  Returns an element instance, representing a processing instruction.
 
+   Note that the element tree XML parser skips over processing
+   instructions in the input instead of creating objects for them. An
+   element tree will thus only contain processing instruction nodes if
+   they have been inserted into to the tree using
+   :meth:`~Element.insert`, :meth:`~Element.append` or
+   :meth:`~Element.extend`.
+
 
 .. function:: register_namespace(prefix, uri)
 
diff --git a/Lib/test/test_xml_etree.py b/Lib/test/test_xml_etree.py
--- a/Lib/test/test_xml_etree.py
+++ b/Lib/test/test_xml_etree.py
@@ -1612,7 +1612,37 @@
         ET.register_namespace('test10777', 'http://myuri/')
         ET.register_namespace('test10777', 'http://myuri/')
 
-
+    def test_pi_treatment(self):
+        root = ET.Element('body', { 'text': 'some text'})
+        root.append(ET.ProcessingInstruction('verb', 'extra data'))
+        tree = ET.ElementTree(root)
+        stream = io.BytesIO()
+        tree.write(stream)
+
+        # PIs are serialized to XML..
+        self.assertIn(b'<?verb extra data?>', bytes(stream.getbuffer())) 
+
+        # ..but skipped when parsing XML
+        stream.seek(0)
+        tree2 = ET.parse(stream)
+        self.assertEqual(len(tree2.getroot().getchildren()), 0)
+
+
+    def test_comment_treatment(self):
+        root = ET.Element('body', { 'text': 'some text'})
+        root.append(ET.Comment('not to be rendered'))
+        tree = ET.ElementTree(root)
+        stream = io.BytesIO()
+        tree.write(stream)
+
+        # PIs are serialized to XML..
+        self.assertIn(b'<!--not to be rendered-->', bytes(stream.getbuffer())) 
+
+        # ..but skipped when parsing XML
+        stream.seek(0)
+        tree2 = ET.parse(stream)
+        self.assertEqual(len(tree2.getroot().getchildren()), 0)
+        
 # --------------------------------------------------------------------