Fixed #129. Footnotes now output valid HTML5.

As HTML5 has depreciated use of `rev=anything` and `rel=footnotes`, they are no
longer inlcuded in the output when the output_format is set to HTML5. Note that
if someone successful registers a spec for `rel=footnotes` in the future (as
a microformat), then that could be considered valid. But until that happens,
it is invlaid to use in HTML5. Therefore, we remove it from the output (when
outputing HTML% only).

As an alternative, two new classes are set (in all output_formats). On the link
to the footnote (where `rel=footnotes` was used), we set `class=footnote-ref`
and on the backlink (where `rev=footnote` was used), we set
`class=footnote-backref`.

Also updated the tests to reflect to the new classes in the output.

4 files changed, 22 insertions, 17 deletions

diff --git a/markdown/extensions/footnotes.py b/markdown/extensions/footnotes.py
index 3d83807..cfe41ed 100644
--- a/markdown/extensions/footnotes.py
+++ b/markdown/extensions/footnotes.py
@@ -61,6 +61,7 @@ class FootnoteExtension(markdown.Extension):
         """ Add pieces to Markdown. """
         md.registerExtension(self)
         self.parser = md.parser
+        self.md = md
         # Insert a preprocessor before ReferencePreprocessor
         md.preprocessors.add("footnote", FootnotePreprocessor(self),
                              "<reference")
@@ -133,7 +134,9 @@ class FootnoteExtension(markdown.Extension):
             self.parser.parseChunk(li, self.footnotes[id])
             backlink = etree.Element("a")
             backlink.set("href", "#" + self.makeFootnoteRefId(id))
-            backlink.set("rev", "footnote")
+            if self.md.output_format not in ['html5', 'xhtml5']:
+                backlink.set("rev", "footnote") # Invalid in HTML5
+            backlink.set("class", "footnote-backref")
             backlink.set("title", "Jump back to footnote %d in the text" % \
                             (self.footnotes.index(id)+1))
             backlink.text = FN_BACKLINK_TEXT
@@ -255,7 +258,9 @@ class FootnotePattern(markdown.inlinepatterns.Pattern):
             a = etree.SubElement(sup, "a")
             sup.set('id', self.footnotes.makeFootnoteRefId(id))
             a.set('href', '#' + self.footnotes.makeFootnoteId(id))
-            a.set('rel', 'footnote')
+            if self.footnotes.md.output_format not in ['html5', 'xhtml5']:
+                a.set('rel', 'footnote') # invalid in HTML5
+            a.set('class', 'footnote-ref')
             a.text = unicode(self.footnotes.footnotes.index(id) + 1)
             return sup
         else:
diff --git a/tests/extensions/extra/footnote.html b/tests/extensions/extra/footnote.html
index 02dcc02..e5b41a7 100644
--- a/tests/extensions/extra/footnote.html
+++ b/tests/extensions/extra/footnote.html
@@ -1,4 +1,4 @@
-<p>This is the body with a footnote<sup id="fnref:1"><a href="#fn:1" rel="footnote">1</a></sup> or two<sup id="fnref:2"><a href="#fn:2" rel="footnote">2</a></sup> or more<sup id="fnref:3"><a href="#fn:3" rel="footnote">3</a></sup> <sup id="fnref:4"><a href="#fn:4" rel="footnote">4</a></sup> <sup id="fnref:5"><a href="#fn:5" rel="footnote">5</a></sup>.</p>
+<p>This is the body with a footnote<sup id="fnref:1"><a class="footnote-ref" href="#fn:1" rel="footnote">1</a></sup> or two<sup id="fnref:2"><a class="footnote-ref" href="#fn:2" rel="footnote">2</a></sup> or more<sup id="fnref:3"><a class="footnote-ref" href="#fn:3" rel="footnote">3</a></sup> <sup id="fnref:4"><a class="footnote-ref" href="#fn:4" rel="footnote">4</a></sup> <sup id="fnref:5"><a class="footnote-ref" href="#fn:5" rel="footnote">5</a></sup>.</p>
 <p>Also a reference that does not exist[^6].</p>
 <div class="footnote">
 <hr />
@@ -9,25 +9,25 @@
 <li>item 1</li>
 <li>item 2</li>
 </ul>
-<p><a href="#fnref:1" rev="footnote" title="Jump back to footnote 1 in the text">&#8617;</a></p>
+<p><a class="footnote-backref" href="#fnref:1" rev="footnote" title="Jump back to footnote 1 in the text">&#8617;</a></p>
 </li>
 <li id="fn:2">
 <blockquote>
 <p>This footnote is a blockquote.</p>
 </blockquote>
-<p><a href="#fnref:2" rev="footnote" title="Jump back to footnote 2 in the text">&#8617;</a></p>
+<p><a class="footnote-backref" href="#fnref:2" rev="footnote" title="Jump back to footnote 2 in the text">&#8617;</a></p>
 </li>
 <li id="fn:3">
-<p>A simple oneliner.&#160;<a href="#fnref:3" rev="footnote" title="Jump back to footnote 3 in the text">&#8617;</a></p>
+<p>A simple oneliner.&#160;<a class="footnote-backref" href="#fnref:3" rev="footnote" title="Jump back to footnote 3 in the text">&#8617;</a></p>
 </li>
 <li id="fn:4">
 <p>A footnote with multiple paragraphs.</p>
-<p>Paragraph two.&#160;<a href="#fnref:4" rev="footnote" title="Jump back to footnote 4 in the text">&#8617;</a></p>
+<p>Paragraph two.&#160;<a class="footnote-backref" href="#fnref:4" rev="footnote" title="Jump back to footnote 4 in the text">&#8617;</a></p>
 </li>
 <li id="fn:5">
 <p>First line of first paragraph.
 Second line of first paragraph is not intended.
-Nor is third...&#160;<a href="#fnref:5" rev="footnote" title="Jump back to footnote 5 in the text">&#8617;</a></p>
+Nor is third...&#160;<a class="footnote-backref" href="#fnref:5" rev="footnote" title="Jump back to footnote 5 in the text">&#8617;</a></p>
 </li>
 </ol>
 </div>
\ No newline at end of file
diff --git a/tests/extensions/extra/footnote_placeholder.html b/tests/extensions/extra/footnote_placeholder.html
index 9c89391..0143145 100644
--- a/tests/extensions/extra/footnote_placeholder.html
+++ b/tests/extensions/extra/footnote_placeholder.html
@@ -2,8 +2,8 @@
 <hr />
 <ol>
 <li id="fn:1">
-<p>A Footnote.&#160;<a href="#fnref:1" rev="footnote" title="Jump back to footnote 1 in the text">&#8617;</a></p>
+<p>A Footnote.&#160;<a class="footnote-backref" href="#fnref:1" rev="footnote" title="Jump back to footnote 1 in the text">&#8617;</a></p>
 </li>
 </ol>
 </div>
-<p>Some text with a footnote<sup id="fnref:1"><a href="#fn:1" rel="footnote">1</a></sup>.</p>
\ No newline at end of file
+<p>Some text with a footnote<sup id="fnref:1"><a class="footnote-ref" href="#fn:1" rel="footnote">1</a></sup>.</p>
\ No newline at end of file
diff --git a/tests/extensions/extra/named_markers.html b/tests/extensions/extra/named_markers.html
index f643b7b..55cea31 100644
--- a/tests/extensions/extra/named_markers.html
+++ b/tests/extensions/extra/named_markers.html
@@ -1,20 +1,20 @@
-<p>This is the body with footnotes<sup id="fnref:foo"><a href="#fn:foo" rel="footnote">1</a></sup> 
-that have named<sup id="fnref:bar"><a href="#fn:bar" rel="footnote">2</a></sup> markers and 
-oddly<sup id="fnref:56"><a href="#fn:56" rel="footnote">3</a></sup>  numbered<sup id="fnref:99"><a href="#fn:99" rel="footnote">4</a></sup> markers.</p>
+<p>This is the body with footnotes<sup id="fnref:foo"><a class="footnote-ref" href="#fn:foo" rel="footnote">1</a></sup> 
+that have named<sup id="fnref:bar"><a class="footnote-ref" href="#fn:bar" rel="footnote">2</a></sup> markers and 
+oddly<sup id="fnref:56"><a class="footnote-ref" href="#fn:56" rel="footnote">3</a></sup>  numbered<sup id="fnref:99"><a class="footnote-ref" href="#fn:99" rel="footnote">4</a></sup> markers.</p>
 <div class="footnote">
 <hr />
 <ol>
 <li id="fn:foo">
-<p>Footnote marked <code>foo</code>.&#160;<a href="#fnref:foo" rev="footnote" title="Jump back to footnote 1 in the text">&#8617;</a></p>
+<p>Footnote marked <code>foo</code>.&#160;<a class="footnote-backref" href="#fnref:foo" rev="footnote" title="Jump back to footnote 1 in the text">&#8617;</a></p>
 </li>
 <li id="fn:bar">
-<p>This one is marked <em>bar</em>.&#160;<a href="#fnref:bar" rev="footnote" title="Jump back to footnote 2 in the text">&#8617;</a></p>
+<p>This one is marked <em>bar</em>.&#160;<a class="footnote-backref" href="#fnref:bar" rev="footnote" title="Jump back to footnote 2 in the text">&#8617;</a></p>
 </li>
 <li id="fn:56">
-<p>A <strong>numbered</strong> footnote.&#160;<a href="#fnref:56" rev="footnote" title="Jump back to footnote 3 in the text">&#8617;</a></p>
+<p>A <strong>numbered</strong> footnote.&#160;<a class="footnote-backref" href="#fnref:56" rev="footnote" title="Jump back to footnote 3 in the text">&#8617;</a></p>
 </li>
 <li id="fn:99">
-<p>The last one.&#160;<a href="#fnref:99" rev="footnote" title="Jump back to footnote 4 in the text">&#8617;</a></p>
+<p>The last one.&#160;<a class="footnote-backref" href="#fnref:99" rev="footnote" title="Jump back to footnote 4 in the text">&#8617;</a></p>
 </li>
 </ol>
 </div>
\ No newline at end of file