diff --git a/tests/s5.basic.html b/tests/s5.basic.html
index 0875d71a7..f0dde094e 100644
--- a/tests/s5.basic.html
+++ b/tests/s5.basic.html
@@ -749,24 +749,24 @@ window.onresize = function(){setTimeout('fontScale()', 50);}</script>
 <div id="currentSlide"></div>
 <div id="header"></div>
 <div id="footer">
-<h1 id="July 15, 2006"
+<h1 id="july 15, 2006"
     >July 15, 2006</h1
-    ><h2 id="My_S5_Document"
+    ><h2 id="my-s5-document"
     >My S5 Document</h2
     ></div>
 </div>
 <div class="presentation">
 
 <div class="slide">
-<h1 id="My_S5_Document-1"
+<h1 id="my-s5-document-1"
     >My S5 Document</h1
-    ><h3 id="Sam Smith, Jen Jones"
+    ><h3 id="sam smith, jen jones"
     >Sam Smith, Jen Jones</h3
-    ><h4 id="July 15, 2006-1"
+    ><h4 id="july 15, 2006-1"
     >July 15, 2006</h4
     ></div>
 <div class="slide">
-<h1 id="First_slide"
+<h1 id="first-slide"
     >First slide</h1
     ><ul
     ><li
@@ -776,7 +776,7 @@ window.onresize = function(){setTimeout('fontScale()', 50);}</script>
       ></ul
     ></div>
 <div class="slide">
-<h1 id="Math"
+<h1 id="math"
     >Math</h1
     ><ul
     ><li
diff --git a/tests/s5.fancy.html b/tests/s5.fancy.html
index 43d489c5a..d3f445d22 100644
--- a/tests/s5.fancy.html
+++ b/tests/s5.fancy.html
@@ -1661,24 +1661,24 @@ else
 <div id="currentSlide"></div>
 <div id="header"></div>
 <div id="footer">
-<h1 id="July 15, 2006"
+<h1 id="july 15, 2006"
     >July 15, 2006</h1
-    ><h2 id="My_S5_Document"
+    ><h2 id="my-s5-document"
     >My S5 Document</h2
     ></div>
 </div>
 <div class="presentation">
 
 <div class="slide">
-<h1 id="My_S5_Document-1"
+<h1 id="my-s5-document-1"
     >My S5 Document</h1
-    ><h3 id="Sam Smith, Jen Jones"
+    ><h3 id="sam smith, jen jones"
     >Sam Smith, Jen Jones</h3
-    ><h4 id="July 15, 2006-1"
+    ><h4 id="july 15, 2006-1"
     >July 15, 2006</h4
     ></div>
 <div class="slide">
-<h1 id="First_slide"
+<h1 id="first-slide"
     >First slide</h1
     ><ul class="incremental"
     ><li
@@ -1688,7 +1688,7 @@ else
       ></ul
     ></div>
 <div class="slide">
-<h1 id="Math"
+<h1 id="math"
     >Math</h1
     ><ul class="incremental"
     ><li
diff --git a/tests/s5.fragment.html b/tests/s5.fragment.html
index bd621c927..505d7d2f6 100644
--- a/tests/s5.fragment.html
+++ b/tests/s5.fragment.html
@@ -1,4 +1,4 @@
-<h1 id="First_slide"
+<h1 id="first-slide"
 >First slide</h1
 ><ul
 ><li
@@ -6,7 +6,7 @@
   ><li
   >second bullet</li
   ></ul
-><h1 id="Math"
+><h1 id="math"
 >Math</h1
 ><ul
 ><li
diff --git a/tests/s5.inserts.html b/tests/s5.inserts.html
index 161472c35..c21ed611a 100644
--- a/tests/s5.inserts.html
+++ b/tests/s5.inserts.html
@@ -15,7 +15,7 @@ STUFF INSERTED
   >STUFF INSERTED
 <h1 class="title"
     >My S5 Document</h1
-    ><h1 id="First_slide"
+    ><h1 id="first-slide"
     >First slide</h1
     ><ul
     ><li
@@ -23,7 +23,7 @@ STUFF INSERTED
       ><li
       >second bullet</li
       ></ul
-    ><h1 id="Math"
+    ><h1 id="math"
     >Math</h1
     ><ul
     ><li
diff --git a/tests/writer.html b/tests/writer.html
index 459047597..a77196578 100644
--- a/tests/writer.html
+++ b/tests/writer.html
@@ -15,36 +15,36 @@
     ><p
     >This is a set of tests for pandoc. Most of them are adapted from John Gruber&rsquo;s markdown test suite.</p
     ><hr
-     /><h1 id="Headers"
+     /><h1 id="headers"
     >Headers</h1
-    ><h2 id="Level_2_with_an_embedded_link"
+    ><h2 id="level-2-with-an-embedded-link"
     >Level 2 with an <a href="/url"
       >embedded link</a
       ></h2
-    ><h3 id="Level_3_with_emphasis"
+    ><h3 id="level-3-with-emphasis"
     >Level 3 with <em
       >emphasis</em
       ></h3
-    ><h4 id="Level_4"
+    ><h4 id="level-4"
     >Level 4</h4
-    ><h5 id="Level_5"
+    ><h5 id="level-5"
     >Level 5</h5
-    ><h1 id="Level_1"
+    ><h1 id="level-1"
     >Level 1</h1
-    ><h2 id="Level_2_with_emphasis"
+    ><h2 id="level-2-with-emphasis"
     >Level 2 with <em
       >emphasis</em
       ></h2
-    ><h3 id="Level_3"
+    ><h3 id="level-3"
     >Level 3</h3
     ><p
     >with no blank line</p
-    ><h2 id="Level_2"
+    ><h2 id="level-2"
     >Level 2</h2
     ><p
     >with no blank line</p
     ><hr
-     /><h1 id="Paragraphs"
+     /><h1 id="paragraphs"
     >Paragraphs</h1
     ><p
     >Here&rsquo;s a regular paragraph.</p
@@ -56,7 +56,7 @@
     >There should be a hard line break<br
        />here.</p
     ><hr
-     /><h1 id="Block_Quotes"
+     /><h1 id="block-quotes"
     >Block Quotes</h1
     ><p
     >E-mail style:</p
@@ -129,7 +129,7 @@
     ><p
     >And a following paragraph.</p
     ><hr
-     /><h1 id="Code_Blocks"
+     /><h1 id="code-blocks"
     >Code Blocks</h1
     ><p
     >Code:</p
@@ -154,9 +154,9 @@ These should not be escaped:  \$ \\ \&gt; \[ \{
 </code
       ></pre
     ><hr
-     /><h1 id="Lists"
+     /><h1 id="lists"
     >Lists</h1
-    ><h2 id="Unordered"
+    ><h2 id="unordered"
     >Unordered</h2
     ><p
     >Asterisks tight:</p
@@ -236,7 +236,7 @@ These should not be escaped:  \$ \\ \&gt; \[ \{
 	>Minus 3</p
 	></li
       ></ul
-    ><h2 id="Ordered"
+    ><h2 id="ordered"
     >Ordered</h2
     ><p
     >Tight:</p
@@ -308,7 +308,7 @@ These should not be escaped:  \$ \\ \&gt; \[ \{
 	>Item 3.</p
 	></li
       ></ol
-    ><h2 id="Nested"
+    ><h2 id="nested"
     >Nested</h2
     ><ul
     ><li
@@ -364,7 +364,7 @@ These should not be escaped:  \$ \\ \&gt; \[ \{
 	>Third</p
 	></li
       ></ol
-    ><h2 id="Tabs_and_spaces"
+    ><h2 id="tabs-and-spaces"
     >Tabs and spaces</h2
     ><ul
     ><li
@@ -387,7 +387,7 @@ These should not be escaped:  \$ \\ \&gt; \[ \{
 	></li
       ></ul
     ><hr
-     /><h1 id="Definition_Lists"
+     /><h1 id="definition-lists"
     >Definition Lists</h1
     ><p
     >Tight using spaces:</p
@@ -474,7 +474,7 @@ These should not be escaped:  \$ \\ \&gt; \[ \{
 	  ></blockquote
 	></dd
       ></dl
-    ><h1 id="HTML_Blocks"
+    ><h1 id="html-blocks"
     >HTML Blocks</h1
     ><p
     >Simple block on one line:</p
@@ -579,7 +579,7 @@ Blah
 
 <hr class="foo" id="bar">
 <hr
-     /><h1 id="Inline_Markup"
+     /><h1 id="inline-markup"
     >Inline Markup</h1
     ><p
     >This is <em
@@ -636,7 +636,7 @@ Blah
       >&lt;html&gt;</code
       >.</p
     ><hr
-     /><h1 id="Smart_quotes,_ellipses,_dashes"
+     /><h1 id="smart-quotes,-ellipses,-dashes"
     >Smart quotes, ellipses, dashes</h1
     ><p
     >&ldquo;Hello,&rdquo; said the spider. &ldquo;&lsquo;Shelob&rsquo; is my name.&rdquo;</p
@@ -659,7 +659,7 @@ Blah
     ><p
     >Ellipses&hellip;and&hellip;and&hellip;.</p
     ><hr
-     /><h1 id="LaTeX"
+     /><h1 id="latex"
     >LaTeX</h1
     ><ul
     ><li
@@ -708,7 +708,7 @@ Dog    &amp; 2      \\
 Cat    &amp; 1      \\ \hline
 \end{tabular}</p
     ><hr
-     /><h1 id="Special_Characters"
+     /><h1 id="special-characters"
     >Special Characters</h1
     ><p
     >Here is some unicode:</p
@@ -767,9 +767,9 @@ Cat    &amp; 1      \\ \hline
     ><p
     >Minus: -</p
     ><hr
-     /><h1 id="Links"
+     /><h1 id="links"
     >Links</h1
-    ><h2 id="Explicit"
+    ><h2 id="explicit"
     >Explicit</h2
     ><p
     >Just a <a href="/url/"
@@ -814,7 +814,7 @@ document.write('<a h'+'ref'+'="ma'+'ilto'+':'+e+'">'+'Email link'+'<\/'+'a'+'>')
     ><a href=""
       >Empty</a
       >.</p
-    ><h2 id="Reference"
+    ><h2 id="reference"
     >Reference</h2
     ><p
     >Foo <a href="/url/"
@@ -863,7 +863,7 @@ document.write('<a h'+'ref'+'="ma'+'ilto'+':'+e+'">'+'Email link'+'<\/'+'a'+'>')
     >Foo <a href="/url/" title="Title with &quot;quote&quot; inside"
       >biz</a
       >.</p
-    ><h2 id="With_ampersands"
+    ><h2 id="with-ampersands"
     >With ampersands</h2
     ><p
     >Here&rsquo;s a <a href="http://example.com/?foo=1&amp;bar=2"
@@ -881,7 +881,7 @@ document.write('<a h'+'ref'+'="ma'+'ilto'+':'+e+'">'+'Email link'+'<\/'+'a'+'>')
     >Here&rsquo;s an <a href="/script?foo=1&amp;bar=2"
       >inline link in pointy braces</a
       >.</p
-    ><h2 id="Autolinks"
+    ><h2 id="autolinks"
     >Autolinks</h2
     ><p
     >With an ampersand: <a href="http://example.com/?foo=1&amp;bar=2"
@@ -924,7 +924,7 @@ document.write('<a h'+'ref'+'="ma'+'ilto'+':'+e+'">'+e+'<\/'+'a'+'>');
 </code
       ></pre
     ><hr
-     /><h1 id="Images"
+     /><h1 id="images"
     >Images</h1
     ><p
     >From &ldquo;Voyage dans la Lune&rdquo; by Georges Melies (1902):</p
@@ -935,7 +935,7 @@ document.write('<a h'+'ref'+'="ma'+'ilto'+':'+e+'">'+e+'<\/'+'a'+'>');
     >Here is a movie <img src="movie.jpg" title="" alt="movie"
        /> icon.</p
     ><hr
-     /><h1 id="Footnotes"
+     /><h1 id="footnotes"
     >Footnotes</h1
     ><p
     >Here is a footnote reference,<a href="#fn1" class="footnoteRef" id="fnref1"