diff --git a/Doc/library/html.parser.rst b/Doc/library/html.parser.rst
index 2bc6555..743d183 100644
--- a/Doc/library/html.parser.rst
+++ b/Doc/library/html.parser.rst
@@ -12,9 +12,13 @@
 This module defines a class :class:`HTMLParser` which serves as the basis for
 parsing text files formatted in HTML (HyperText Mark-up Language) and XHTML.
 
-.. class:: HTMLParser()
+.. class:: HTMLParser(strict=True)
 
-   The :class:`HTMLParser` class is instantiated without arguments.
+   Create a parser instance.  If *strict* is ``True`` (the default), invalid
+   html results in :exc:`~html.parser.HTMLParseError` exceptions [#]_.  If
+   *strict* is ``False``, the parser uses heuristics to make a best guess at
+   the intention of any invalid html it encounters, similar to the way most
+   browsers do.
 
    An :class:`HTMLParser` instance is fed HTML data and calls handler functions when tags
    begin and end.  The :class:`HTMLParser` class is meant to be overridden by the
@@ -191,3 +195,8 @@
    Encountered a html end tag
 
 
+.. rubric:: Footnotes
+
+.. [#] For backward compatibility reasons *strict* mode does not throw
+       errors for all non-compliant HTML.  That is, some invalid HTML
+       is tolerated even in *strict* mode.
diff --git a/Lib/html/parser.py b/Lib/html/parser.py
index c2c7f6b..8d275ab 100644
--- a/Lib/html/parser.py
+++ b/Lib/html/parser.py
@@ -24,10 +24,14 @@
 piclose = re.compile('>')
 commentclose = re.compile(r'--\s*>')
 tagfind = re.compile('[a-zA-Z][-.a-zA-Z0-9:_]*')
+# Note, the strict one of this pair isn't really strict, but we can't
+# make it correctly strict without breaking backward compatibility.
 attrfind = re.compile(
     r'\s*([a-zA-Z_][-.:a-zA-Z_0-9]*)(\s*=\s*'
     r'(\'[^\']*\'|"[^"]*"|[-a-zA-Z0-9./,:;+*%?!&$\(\)_#=~@]*))?')
-
+attrfind_tolerant = re.compile(
+    r'\s*([a-zA-Z_][-.:a-zA-Z_0-9]*)(\s*=\s*'
+    r'(\'[^\']*\'|"[^"]*"|[^>\s]*))?')
 locatestarttagend = re.compile(r"""
   <[a-zA-Z][-.a-zA-Z0-9:_]*          # tag name
   (?:\s+                             # whitespace before attribute name
@@ -42,6 +46,21 @@
    )*
   \s*                                # trailing whitespace
 """, re.VERBOSE)
+locatestarttagend_tolerant = re.compile(r"""
+  <[a-zA-Z][-.a-zA-Z0-9:_]*          # tag name
+  (?:\s*                             # optional whitespace before attribute name
+    (?:[a-zA-Z_][-.:a-zA-Z0-9_]*     # attribute name
+      (?:\s*=\s*                     # value indicator
+        (?:'[^']*'                   # LITA-enclosed value
+          |\"[^\"]*\"                # LIT-enclosed value
+          |[^'\">\s]+                # bare value
+         )
+         (?:\s*,)*                   # possibly followed by a comma
+       )?
+     )
+   )*
+  \s*                                # trailing whitespace
+""", re.VERBOSE)
 endendtag = re.compile('>')
 endtagfind = re.compile('</\s*([a-zA-Z][-.a-zA-Z0-9:_]*)\s*>')
 
@@ -86,9 +105,15 @@
 
     CDATA_CONTENT_ELEMENTS = ("script", "style")
 
+    def __init__(self, strict=True):
+        """Initialize and reset this instance.
 
-    def __init__(self):
-        """Initialize and reset this instance."""
+        If strict is set to True (the default), errors are raised when invalid
+        HTML is encountered.  If set to False, an attempt is instead made to
+        continue parsing, making "best guesses" about the intended meaning, in
+        a fashion similar to what browsers typically do.
+        """
+        self.strict = strict
         self.reset()
 
     def reset(self):
@@ -160,9 +185,18 @@
                 else:
                     break
                 if k < 0:
-                    if end:
+                    if not end:
+                        break
+                    if self.strict:
                         self.error("EOF in middle of construct")
-                    break
+                    k = rawdata.find('>', i + 1)
+                    if k < 0:
+                        k = rawdata.find('<', i + 1)
+                        if k < 0:
+                            k = i + 1
+                    else:
+                        k += 1
+                    self.handle_data(rawdata[i:k])
                 i = self.updatepos(i, k)
             elif startswith("&#", i):
                 match = charref.match(rawdata, i)
@@ -193,7 +227,12 @@
                 if match:
                     # match.group() will contain at least 2 chars
                     if end and match.group() == rawdata[i:]:
-                        self.error("EOF in middle of entity or char ref")
+                        if self.strict:
+                            self.error("EOF in middle of entity or char ref")
+                        else:
+                            if k <= i:
+                                k = n
+                            i = self.updatepos(i, i + 1)
                     # incomplete
                     break
                 elif (i + 1) < n:
@@ -240,7 +279,10 @@
         self.lasttag = tag = rawdata[i+1:k].lower()
 
         while k < endpos:
-            m = attrfind.match(rawdata, k)
+            if self.strict:
+                m = attrfind.match(rawdata, k)
+            else:
+                m = attrfind_tolerant.search(rawdata, k)
             if not m:
                 break
             attrname, rest, attrvalue = m.group(1, 2, 3)
@@ -262,8 +304,11 @@
                          - self.__starttag_text.rfind("\n")
             else:
                 offset = offset + len(self.__starttag_text)
-            self.error("junk characters in start tag: %r"
-                       % (rawdata[k:endpos][:20],))
+            if self.strict:
+                self.error("junk characters in start tag: %r"
+                           % (rawdata[k:endpos][:20],))
+            self.handle_data(rawdata[i:endpos])
+            return endpos
         if end.endswith('/>'):
             # XHTML-style empty tag: <span attr="value" />
             self.handle_startendtag(tag, attrs)
@@ -277,7 +322,10 @@
     # or -1 if incomplete.
     def check_for_whole_start_tag(self, i):
         rawdata = self.rawdata
-        m = locatestarttagend.match(rawdata, i)
+        if self.strict:
+            m = locatestarttagend.match(rawdata, i)
+        else:
+            m = locatestarttagend_tolerant.match(rawdata, i)
         if m:
             j = m.end()
             next = rawdata[j:j+1]
@@ -290,8 +338,13 @@
                     # buffer boundary
                     return -1
                 # else bogus input
-                self.updatepos(i, j + 1)
-                self.error("malformed empty start tag")
+                if self.strict:
+                    self.updatepos(i, j + 1)
+                    self.error("malformed empty start tag")
+                if j > i:
+                    return j
+                else:
+                    return i + 1
             if next == "":
                 # end of input
                 return -1
@@ -300,8 +353,13 @@
                 # end of input in or before attribute value, or we have the
                 # '/' from a '/>' ending
                 return -1
-            self.updatepos(i, j)
-            self.error("malformed start tag")
+            if self.strict:
+                self.updatepos(i, j)
+                self.error("malformed start tag")
+            if j > i:
+                return j
+            else:
+                return i + 1
         raise AssertionError("we should not get here!")
 
     # Internal -- parse endtag, return end or -1 if incomplete
@@ -314,7 +372,15 @@
         j = match.end()
         match = endtagfind.match(rawdata, i) # </ + tag + >
         if not match:
-            self.error("bad end tag: %r" % (rawdata[i:j],))
+            if self.strict:
+                self.error("bad end tag: %r" % (rawdata[i:j],))
+            k = rawdata.find('<', i + 1, j)
+            if k > i:
+                j = k
+            if j <= i:
+                j = i + 1
+            self.handle_data(rawdata[i:j])
+            return j
         tag = match.group(1)
         self.handle_endtag(tag.lower())
         self.clear_cdata_mode()
@@ -358,7 +424,8 @@
         pass
 
     def unknown_decl(self, data):
-        self.error("unknown declaration: %r" % (data,))
+        if self.strict:
+            self.error("unknown declaration: %r" % (data,))
 
     # Internal -- helper to remove special character quoting
     entitydefs = None
diff --git a/Lib/test/test_htmlparser.py b/Lib/test/test_htmlparser.py
index e982218..beaf6b6 100644
--- a/Lib/test/test_htmlparser.py
+++ b/Lib/test/test_htmlparser.py
@@ -8,10 +8,10 @@
 
 class EventCollector(html.parser.HTMLParser):
 
-    def __init__(self):
+    def __init__(self, *args, **kw):
         self.events = []
         self.append = self.events.append
-        html.parser.HTMLParser.__init__(self)
+        html.parser.HTMLParser.__init__(self, *args, **kw)
 
     def get_events(self):
         # Normalize the list of events so that buffer artefacts don't
@@ -72,8 +72,10 @@
 
 class TestCaseBase(unittest.TestCase):
 
-    def _run_check(self, source, expected_events, collector=EventCollector):
-        parser = collector()
+    def _run_check(self, source, expected_events, collector=None):
+        if collector is None:
+            collector = EventCollector()
+        parser = collector
         for s in source:
             parser.feed(s)
         parser.close()
@@ -84,7 +86,7 @@
                       "\nReceived:\n" + pprint.pformat(events))
 
     def _run_check_extra(self, source, events):
-        self._run_check(source, events, EventCollectorExtra)
+        self._run_check(source, events, EventCollectorExtra())
 
     def _parse_error(self, source):
         def parse(source=source):
@@ -321,8 +323,42 @@
                 ])
 
 
+class HTMLParserTolerantTestCase(TestCaseBase):
+
+    def setUp(self):
+        self.collector = EventCollector(strict=False)
+
+    def test_tolerant_parsing(self):
+        self._run_check('<html <html>te>>xt&a<<bc</a></html>\n'
+                        '<img src="URL><//img></html</html>', [
+                             ('data', '<html '),
+                             ('starttag', 'html', []),
+                             ('data', 'te>>xt'),
+                             ('entityref', 'a'),
+                             ('data', '<<bc'),
+                             ('endtag', 'a'),
+                             ('endtag', 'html'),
+                             ('data', '\n<img src="URL><//img></html'),
+                             ('endtag', 'html')],
+                        collector = self.collector)
+
+    def test_comma_between_attributes(self):
+        self._run_check('<form action="/xxx.php?a=1&amp;b=2&amp", '
+                        'method="post">', [
+                            ('starttag', 'form',
+                                [('action', '/xxx.php?a=1&b=2&amp'),
+                                 ('method', 'post')])],
+                        collector = self.collector)
+
+    def test_weird_chars_in_unquoted_attribute_values(self):
+        self._run_check('<form action=bogus|&#()value>', [
+                            ('starttag', 'form',
+                                [('action', 'bogus|&#()value')])],
+                        collector = self.collector)
+
+
 def test_main():
-    support.run_unittest(HTMLParserTestCase)
+    support.run_unittest(HTMLParserTestCase, HTMLParserTolerantTestCase)
 
 
 if __name__ == "__main__":
diff --git a/Misc/NEWS b/Misc/NEWS
index 434ed23..7c5d8d1 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -58,6 +58,9 @@
 Library
 -------
 
+- Issue #1486713: HTMLParser now has an optional tolerant mode where it
+  tries to guess at the correct parsing of invalid html.
+
 - Issue #10554: Add context manager support to subprocess.Popen objects.
 
 - Issue #8989: email.utils.make_msgid now has a domain parameter that can