Modified the HTML writer to add invisible anchors to each section

heading.  The anchors are derived form the text of the section
heading as described in README.  This makes it easy to insert
links that jump from one part of a document to another:
for example, '[back to the Introduction](#Introduction)'.


git-svn-id: https://pandoc.googlecode.com/svn/trunk@246 788f1e2b-df1e-0410-8736-df70ead52e1b

8 files changed, 108 insertions, 6 deletions

diff --git a/README b/README
index 8a75d90da..d64654376 100644
--- a/README
+++ b/README
@@ -261,6 +261,26 @@ markdown test suite, type `make test-markdown`.)
 
 [standard markdown]:  http://daringfireball.net/projects/markdown/syntax
 
+## Section Headings
+
+Pandoc creates an invisible anchor in front of every HTML section
+heading.  The ID of this anchor is derived from the section heading
+itself:  spaces are converted to underscores, and formatting, links,
+and other markup are removed.  Thus, for example, the source
+
+    ## Aristotle's *De Anima*
+
+gets converted to HTML as follows:
+
+    <a id="Aristotle's_De_Anima"></a>
+    <h2>Aristotle's <em>De Anima</em></h2>
+
+This makes it easy to provide internal links that jump to a particular
+place in a document.  To provide a link to the heading above, for
+example, just insert:
+
+    [Back to Aristotle](#Aristotle's_De_Anima)
+
 ## Lists
 
 Pandoc behaves differently from standard markdown on some "edge
diff --git a/src/Text/Pandoc/Writers/HTML.hs b/src/Text/Pandoc/Writers/HTML.hs
index f1bd0f8b5..7ba506acb 100644
--- a/src/Text/Pandoc/Writers/HTML.hs
+++ b/src/Text/Pandoc/Writers/HTML.hs
@@ -154,12 +154,14 @@ blockToHtml options (OrderedList lst) =
     let attribs = if (writerIncremental options) then " class=\"incremental\"" else "" in
     "<ol" ++ attribs ++ ">\n" ++ (concatMap (listItemToHtml options) lst) ++ "</ol>\n"
 blockToHtml options HorizontalRule = "<hr />\n"
-blockToHtml options (Header level lst) = if ((level > 0) && (level <= 6)) then
-                                             "<h" ++ (show level) ++ ">" ++ 
-                                                      (inlineListToHtml options lst) ++ 
-                                                      "</h" ++ (show level) ++ ">\n"
-                                         else 
-                                             "<p>" ++ (inlineListToHtml options lst) ++ "</p>\n"
+blockToHtml options (Header level lst) = 
+    let contents = inlineListToHtml options lst in
+    let simplify = gsub "<[^>]*>" ""  . gsub " " "_" in
+    if ((level > 0) && (level <= 6))
+        then "<a id=\"" ++ simplify contents ++ "\"></a>\n" ++
+             "<h" ++ (show level) ++ ">" ++ contents ++ 
+             "</h" ++ (show level) ++ ">\n"
+        else "<p>" ++ contents ++ "</p>\n"
 listItemToHtml options list = "<li>" ++ (concatMap (blockToHtml options) list) ++ "</li>\n"
 
 -- | Convert list of Pandoc inline elements to HTML.
diff --git a/tests/s5.basic.html b/tests/s5.basic.html
index 919b09da6..88510a74c 100644
--- a/tests/s5.basic.html
+++ b/tests/s5.basic.html
@@ -723,18 +723,24 @@ window.onresize = function(){setTimeout('fontScale()', 50);}</script>
 <div id="currentSlide"></div>
 <div id="header"></div>
 <div id="footer">
+<a id="July_15,_2006"></a>
 <h1>July 15, 2006</h1>
+<a id="My_S5_Document"></a>
 <h2>My S5 Document</h2>
 </div>
 </div>
 <div class="presentation">
 
 <div class="slide">
+<a id="My_S5_Document"></a>
 <h1>My S5 Document</h1>
+<a id="Sam_Smith,_Jen_Jones"></a>
 <h3>Sam Smith, Jen Jones</h3>
+<a id="July_15,_2006"></a>
 <h4>July 15, 2006</h4>
 </div>
 <div class="slide">
+<a id="First_slide"></a>
 <h1>First slide</h1>
 <ul>
 <li>first bullet</li>
@@ -742,6 +748,7 @@ window.onresize = function(){setTimeout('fontScale()', 50);}</script>
 </ul>
 </div>
 <div class="slide">
+<a id="Smarty"></a>
 <h1>Smarty</h1>
 <ul class="incremental">
 <li>"Hello there"</li>
@@ -750,6 +757,7 @@ window.onresize = function(){setTimeout('fontScale()', 50);}</script>
 </ul>
 </div>
 <div class="slide">
+<a id="Math"></a>
 <h1>Math</h1>
 <ul>
 <li>$\frac{d}{dx}f(x)=\lim_{h\to 0}\frac{f(x+h)-f(x)}{h}$</li>
diff --git a/tests/s5.fancy.html b/tests/s5.fancy.html
index 8686a8542..e015f7b99 100644
--- a/tests/s5.fancy.html
+++ b/tests/s5.fancy.html
@@ -1635,18 +1635,24 @@ else
 <div id="currentSlide"></div>
 <div id="header"></div>
 <div id="footer">
+<a id="July_15,_2006"></a>
 <h1>July 15, 2006</h1>
+<a id="My_S5_Document"></a>
 <h2>My S5 Document</h2>
 </div>
 </div>
 <div class="presentation">
 
 <div class="slide">
+<a id="My_S5_Document"></a>
 <h1>My S5 Document</h1>
+<a id="Sam_Smith,_Jen_Jones"></a>
 <h3>Sam Smith, Jen Jones</h3>
+<a id="July_15,_2006"></a>
 <h4>July 15, 2006</h4>
 </div>
 <div class="slide">
+<a id="First_slide"></a>
 <h1>First slide</h1>
 <ul class="incremental">
 <li>first bullet</li>
@@ -1654,6 +1660,7 @@ else
 </ul>
 </div>
 <div class="slide">
+<a id="Smarty"></a>
 <h1>Smarty</h1>
 <ul>
 <li>&ldquo;Hello there&rdquo;</li>
@@ -1662,6 +1669,7 @@ else
 </ul>
 </div>
 <div class="slide">
+<a id="Math"></a>
 <h1>Math</h1>
 <ul class="incremental">
 <li>$\frac{d}{dx}f(x)=\lim_{h\to 0}\frac{f(x+h)-f(x)}{h}$</li>
diff --git a/tests/s5.fragment.html b/tests/s5.fragment.html
index 370b9c111..240bafb35 100644
--- a/tests/s5.fragment.html
+++ b/tests/s5.fragment.html
@@ -1,8 +1,10 @@
+<a id="First_slide"></a>
 <h1>First slide</h1>
 <ul>
 <li>first bullet</li>
 <li>second bullet</li>
 </ul>
+<a id="Smarty"></a>
 <h1>Smarty</h1>
 <blockquote>
 <ul>
@@ -11,6 +13,7 @@
 <li>And 'ellipses'...</li>
 </ul>
 </blockquote>
+<a id="Math"></a>
 <h1>Math</h1>
 <ul>
 <li>$\frac{d}{dx}f(x)=\lim_{h\to 0}\frac{f(x+h)-f(x)}{h}$</li>
diff --git a/tests/s5.inserts.html b/tests/s5.inserts.html
index 7be33a2c8..ba6ae5f48 100644
--- a/tests/s5.inserts.html
+++ b/tests/s5.inserts.html
@@ -13,11 +13,13 @@ STUFF INSERTED
 <body>
 STUFF INSERTED
 <h1 class="title">My S5 Document</h1>
+<a id="First_slide"></a>
 <h1>First slide</h1>
 <ul>
 <li>first bullet</li>
 <li>second bullet</li>
 </ul>
+<a id="Smarty"></a>
 <h1>Smarty</h1>
 <blockquote>
 <ul>
@@ -26,6 +28,7 @@ STUFF INSERTED
 <li>And 'ellipses'...</li>
 </ul>
 </blockquote>
+<a id="Math"></a>
 <h1>Math</h1>
 <ul>
 <li>$\frac{d}{dx}f(x)=\lim_{h\to 0}\frac{f(x+h)-f(x)}{h}$</li>
diff --git a/tests/writer.html b/tests/writer.html
index 6fcb949ec..0661fb732 100644
--- a/tests/writer.html
+++ b/tests/writer.html
@@ -12,18 +12,28 @@
 <h1 class="title">Pandoc Test Suite</h1>
 <p>This is a set of tests for pandoc. Most of them are adapted from John Gruber's markdown test suite.</p>
 <hr />
+<a id="Headers"></a>
 <h1>Headers</h1>
+<a id="Level_2_with_an_embedded_link"></a>
 <h2>Level 2 with an <a href="/url">embedded link</a></h2>
+<a id="Level_3_with_emphasis"></a>
 <h3>Level 3 with <em>emphasis</em></h3>
+<a id="Level_4"></a>
 <h4>Level 4</h4>
+<a id="Level_5"></a>
 <h5>Level 5</h5>
+<a id="Level_1"></a>
 <h1>Level 1</h1>
+<a id="Level_2_with_emphasis"></a>
 <h2>Level 2 with <em>emphasis</em></h2>
+<a id="Level_3"></a>
 <h3>Level 3</h3>
 <p>with no blank line</p>
+<a id="Level_2"></a>
 <h2>Level 2</h2>
 <p>with no blank line</p>
 <hr />
+<a id="Paragraphs"></a>
 <h1>Paragraphs</h1>
 <p>Here's a regular paragraph.</p>
 <p>In Markdown 1.0.0 and earlier. Version 8. This line turns into a list item. Because a hard-wrapped line in the middle of a paragraph looked like a list item.</p>
@@ -31,6 +41,7 @@
 <p>There should be a hard line break<br />
 here.</p>
 <hr />
+<a id="Block_Quotes"></a>
 <h1>Block Quotes</h1>
 <p>E-mail style:</p>
 <blockquote>
@@ -79,6 +90,7 @@ here.</p>
 </blockquote>
 <p>And a following paragraph.</p>
 <hr />
+<a id="Code_Blocks"></a>
 <h1>Code Blocks</h1>
 <p>Code:</p>
 <pre><code>---- (should be four hyphens)
@@ -95,7 +107,9 @@ this code block is indented by one tab
 These should not be escaped:  \$ \\ \> \[ \{
 </code></pre>
 <hr />
+<a id="Lists"></a>
 <h1>Lists</h1>
+<a id="Unordered"></a>
 <h2>Unordered</h2>
 <p>Asterisks tight:</p>
 <ul>
@@ -142,6 +156,7 @@ These should not be escaped:  \$ \\ \> \[ \{
 <li><p>Minus 3</p>
 </li>
 </ul>
+<a id="Ordered"></a>
 <h2>Ordered</h2>
 <p>Tight:</p>
 <ol>
@@ -183,6 +198,7 @@ These should not be escaped:  \$ \\ \> \[ \{
 <li><p>Item 3.</p>
 </li>
 </ol>
+<a id="Nested"></a>
 <h2>Nested</h2>
 <ul>
 <li>Tab<ul>
@@ -218,6 +234,7 @@ These should not be escaped:  \$ \\ \> \[ \{
 <li><p>Third</p>
 </li>
 </ol>
+<a id="Tabs_and_spaces"></a>
 <h2>Tabs and spaces</h2>
 <ul>
 <li><p>this is a list item indented with tabs</p>
@@ -232,6 +249,7 @@ These should not be escaped:  \$ \\ \> \[ \{
 </li>
 </ul>
 <hr />
+<a id="HTML_Blocks"></a>
 <h1>HTML Blocks</h1>
 <p>Simple block on one line:</p>
 <div>foo</div>
@@ -307,6 +325,7 @@ Blah
 
 <hr class="foo" id="bar">
 <hr />
+<a id="Inline_Markup"></a>
 <h1>Inline Markup</h1>
 <p>This is <em>emphasized</em>, and so <em>is this</em>.</p>
 <p>This is <strong>strong</strong>, and so <strong>is this</strong>.</p>
@@ -317,6 +336,7 @@ Blah
 <p>So is <strong><em>this</em></strong> word.</p>
 <p>This is code: <code>></code>, <code>$</code>, <code>\</code>, <code>\$</code>, <code>&lt;html></code>.</p>
 <hr />
+<a id="Smart_quotes,_ellipses,_dashes"></a>
 <h1>Smart quotes, ellipses, dashes</h1>
 <p>"Hello," said the spider. "'Shelob' is my name."</p>
 <p>'A', 'B', and 'C' are letters.</p>
@@ -327,6 +347,7 @@ Blah
 <p>Dashes between numbers: 5-7, 255-66, 1987-1999.</p>
 <p>Ellipses...and. . .and . . . .</p>
 <hr />
+<a id="LaTeX"></a>
 <h1>LaTeX</h1>
 <ul>
 <li>\cite[22-23]{smith.1899}</li>
@@ -352,6 +373,7 @@ Dog    &amp; 2      \\
 Cat    &amp; 1      \\ \hline
 \end{tabular}</p>
 <hr />
+<a id="Special_Characters"></a>
 <h1>Special Characters</h1>
 <p>Here is some unicode:</p>
 <ul>
@@ -383,7 +405,9 @@ Cat    &amp; 1      \\ \hline
 <p>Plus: +</p>
 <p>Minus: -</p>
 <hr />
+<a id="Links"></a>
 <h1>Links</h1>
+<a id="Explicit"></a>
 <h2>Explicit</h2>
 <p>Just a <a href="/url/">URL</a>.</p>
 <p><a href="/url/" title="title">URL and title</a>.</p>
@@ -393,6 +417,7 @@ Cat    &amp; 1      \\ \hline
 <p><a href="/url/" title="title with single quotes">URL and title</a></p>
 <p><script type="text/javascript">h='nowhere.net';n='nobody';e=n+'@'+h;document.write('<a href="mailto:'+e+'">'+'Email link'+'<\/a>');</script><noscript>Email link (nobody [at] nowhere.net)</noscript></p>
 <p><a href="">Empty</a>.</p>
+<a id="Reference"></a>
 <h2>Reference</h2>
 <p>Foo <a href="/url/">bar</a>.</p>
 <p>Foo <a href="/url/">bar</a>.</p>
@@ -407,11 +432,13 @@ Cat    &amp; 1      \\ \hline
 </code></pre>
 <p>Foo <a href="/url/" title="Title with &quot;quotes&quot; inside">bar</a>.</p>
 <p>Foo <a href="/url/" title="Title with &quot;quote&quot; inside">biz</a>.</p>
+<a id="With_ampersands"></a>
 <h2>With ampersands</h2>
 <p>Here's a <a href="http://example.com/?foo=1&amp;bar=2">link with an ampersand in the URL</a>.</p>
 <p>Here's a link with an amersand in the link text: <a href="http://att.com/" title="AT&T">AT&amp;T</a>.</p>
 <p>Here's an <a href="/script?foo=1&amp;bar=2">inline link</a>.</p>
 <p>Here's an <a href="/script?foo=1&amp;bar=2">inline link in pointy braces</a>.</p>
+<a id="Autolinks"></a>
 <h2>Autolinks</h2>
 <p>With an ampersand: <a href="http://example.com/?foo=1&amp;bar=2">http://example.com/?foo=1&amp;bar=2</a></p>
 <ul>
@@ -427,11 +454,13 @@ Cat    &amp; 1      \\ \hline
 <pre><code>or here: &lt;http://example.com/>
 </code></pre>
 <hr />
+<a id="Images"></a>
 <h1>Images</h1>
 <p>From "Voyage dans la Lune" by Georges Melies (1902):</p>
 <p><img src="lalune.jpg" title="Voyage dans la Lune" alt="lalune"></p>
 <p>Here is a movie <img src="movie.jpg" alt="movie"> icon.</p>
 <hr />
+<a id="Footnotes"></a>
 <h1>Footnotes</h1>
 <p>Here is a footnote reference,<sup class="footnoteRef" id="fnref1"><a href="#fn1">1</a></sup> and another.<sup class="footnoteRef" id="fnref2"><a href="#fn2">2</a></sup> This should <em>not</em> be a footnote reference, because it contains a space.[^my note] Here is an inline note.<sup class="footnoteRef" id="fnref3"><a href="#fn3">3</a></sup></p>
 <p>This paragraph should not be part of the note, as it is not indented.</p>
diff --git a/tests/writer.smart.html b/tests/writer.smart.html
index 508b0abf5..d5fb3da93 100644
--- a/tests/writer.smart.html
+++ b/tests/writer.smart.html
@@ -12,18 +12,28 @@
 <h1 class="title">Pandoc Test Suite</h1>
 <p>This is a set of tests for pandoc. Most of them are adapted from John Gruber&rsquo;s markdown test suite.</p>
 <hr />
+<a id="Headers"></a>
 <h1>Headers</h1>
+<a id="Level_2_with_an_embedded_link"></a>
 <h2>Level 2 with an <a href="/url">embedded link</a></h2>
+<a id="Level_3_with_emphasis"></a>
 <h3>Level 3 with <em>emphasis</em></h3>
+<a id="Level_4"></a>
 <h4>Level 4</h4>
+<a id="Level_5"></a>
 <h5>Level 5</h5>
+<a id="Level_1"></a>
 <h1>Level 1</h1>
+<a id="Level_2_with_emphasis"></a>
 <h2>Level 2 with <em>emphasis</em></h2>
+<a id="Level_3"></a>
 <h3>Level 3</h3>
 <p>with no blank line</p>
+<a id="Level_2"></a>
 <h2>Level 2</h2>
 <p>with no blank line</p>
 <hr />
+<a id="Paragraphs"></a>
 <h1>Paragraphs</h1>
 <p>Here&rsquo;s a regular paragraph.</p>
 <p>In Markdown 1.0.0 and earlier. Version 8. This line turns into a list item. Because a hard-wrapped line in the middle of a paragraph looked like a list item.</p>
@@ -31,6 +41,7 @@
 <p>There should be a hard line break<br />
 here.</p>
 <hr />
+<a id="Block_Quotes"></a>
 <h1>Block Quotes</h1>
 <p>E-mail style:</p>
 <blockquote>
@@ -79,6 +90,7 @@ here.</p>
 </blockquote>
 <p>And a following paragraph.</p>
 <hr />
+<a id="Code_Blocks"></a>
 <h1>Code Blocks</h1>
 <p>Code:</p>
 <pre><code>---- (should be four hyphens)
@@ -95,7 +107,9 @@ this code block is indented by one tab
 These should not be escaped:  \$ \\ \> \[ \{
 </code></pre>
 <hr />
+<a id="Lists"></a>
 <h1>Lists</h1>
+<a id="Unordered"></a>
 <h2>Unordered</h2>
 <p>Asterisks tight:</p>
 <ul>
@@ -142,6 +156,7 @@ These should not be escaped:  \$ \\ \> \[ \{
 <li><p>Minus 3</p>
 </li>
 </ul>
+<a id="Ordered"></a>
 <h2>Ordered</h2>
 <p>Tight:</p>
 <ol>
@@ -183,6 +198,7 @@ These should not be escaped:  \$ \\ \> \[ \{
 <li><p>Item 3.</p>
 </li>
 </ol>
+<a id="Nested"></a>
 <h2>Nested</h2>
 <ul>
 <li>Tab<ul>
@@ -218,6 +234,7 @@ These should not be escaped:  \$ \\ \> \[ \{
 <li><p>Third</p>
 </li>
 </ol>
+<a id="Tabs_and_spaces"></a>
 <h2>Tabs and spaces</h2>
 <ul>
 <li><p>this is a list item indented with tabs</p>
@@ -232,6 +249,7 @@ These should not be escaped:  \$ \\ \> \[ \{
 </li>
 </ul>
 <hr />
+<a id="HTML_Blocks"></a>
 <h1>HTML Blocks</h1>
 <p>Simple block on one line:</p>
 <div>foo</div>
@@ -307,6 +325,7 @@ Blah
 
 <hr class="foo" id="bar">
 <hr />
+<a id="Inline_Markup"></a>
 <h1>Inline Markup</h1>
 <p>This is <em>emphasized</em>, and so <em>is this</em>.</p>
 <p>This is <strong>strong</strong>, and so <strong>is this</strong>.</p>
@@ -317,6 +336,7 @@ Blah
 <p>So is <strong><em>this</em></strong> word.</p>
 <p>This is code: <code>></code>, <code>$</code>, <code>\</code>, <code>\$</code>, <code>&lt;html></code>.</p>
 <hr />
+<a id="Smart_quotes,_ellipses,_dashes"></a>
 <h1>Smart quotes, ellipses, dashes</h1>
 <p>&ldquo;Hello,&rdquo; said the spider. &ldquo;&lsquo;Shelob&rsquo; is my name.&rdquo;</p>
 <p>&lsquo;A&rsquo;, &lsquo;B&rsquo;, and &lsquo;C&rsquo; are letters.</p>
@@ -327,6 +347,7 @@ Blah
 <p>Dashes between numbers: 5&ndash;7, 255&ndash;66, 1987&ndash;1999.</p>
 <p>Ellipses&hellip;and&hellip;and &hellip; .</p>
 <hr />
+<a id="LaTeX"></a>
 <h1>LaTeX</h1>
 <ul>
 <li>\cite[22-23]{smith.1899}</li>
@@ -352,6 +373,7 @@ Dog    &amp; 2      \\
 Cat    &amp; 1      \\ \hline
 \end{tabular}</p>
 <hr />
+<a id="Special_Characters"></a>
 <h1>Special Characters</h1>
 <p>Here is some unicode:</p>
 <ul>
@@ -383,7 +405,9 @@ Cat    &amp; 1      \\ \hline
 <p>Plus: +</p>
 <p>Minus: -</p>
 <hr />
+<a id="Links"></a>
 <h1>Links</h1>
+<a id="Explicit"></a>
 <h2>Explicit</h2>
 <p>Just a <a href="/url/">URL</a>.</p>
 <p><a href="/url/" title="title">URL and title</a>.</p>
@@ -393,6 +417,7 @@ Cat    &amp; 1      \\ \hline
 <p><a href="/url/" title="title with single quotes">URL and title</a></p>
 <p><script type="text/javascript">h='nowhere.net';n='nobody';e=n+'@'+h;document.write('<a href="mailto:'+e+'">'+'Email link'+'<\/a>');</script><noscript>Email link (nobody [at] nowhere.net)</noscript></p>
 <p><a href="">Empty</a>.</p>
+<a id="Reference"></a>
 <h2>Reference</h2>
 <p>Foo <a href="/url/">bar</a>.</p>
 <p>Foo <a href="/url/">bar</a>.</p>
@@ -407,11 +432,13 @@ Cat    &amp; 1      \\ \hline
 </code></pre>
 <p>Foo <a href="/url/" title="Title with &quot;quotes&quot; inside">bar</a>.</p>
 <p>Foo <a href="/url/" title="Title with &quot;quote&quot; inside">biz</a>.</p>
+<a id="With_ampersands"></a>
 <h2>With ampersands</h2>
 <p>Here&rsquo;s a <a href="http://example.com/?foo=1&amp;bar=2">link with an ampersand in the URL</a>.</p>
 <p>Here&rsquo;s a link with an amersand in the link text: <a href="http://att.com/" title="AT&T">AT&amp;T</a>.</p>
 <p>Here&rsquo;s an <a href="/script?foo=1&amp;bar=2">inline link</a>.</p>
 <p>Here&rsquo;s an <a href="/script?foo=1&amp;bar=2">inline link in pointy braces</a>.</p>
+<a id="Autolinks"></a>
 <h2>Autolinks</h2>
 <p>With an ampersand: <a href="http://example.com/?foo=1&amp;bar=2">http://example.com/?foo=1&amp;bar=2</a></p>
 <ul>
@@ -427,11 +454,13 @@ Cat    &amp; 1      \\ \hline
 <pre><code>or here: &lt;http://example.com/>
 </code></pre>
 <hr />
+<a id="Images"></a>
 <h1>Images</h1>
 <p>From &ldquo;Voyage dans la Lune&rdquo; by Georges Melies (1902):</p>
 <p><img src="lalune.jpg" title="Voyage dans la Lune" alt="lalune"></p>
 <p>Here is a movie <img src="movie.jpg" alt="movie"> icon.</p>
 <hr />
+<a id="Footnotes"></a>
 <h1>Footnotes</h1>
 <p>Here is a footnote reference,<sup class="footnoteRef" id="fnref1"><a href="#fn1">1</a></sup> and another.<sup class="footnoteRef" id="fnref2"><a href="#fn2">2</a></sup> This should <em>not</em> be a footnote reference, because it contains a space.[^my note] Here is an inline note.<sup class="footnoteRef" id="fnref3"><a href="#fn3">3</a></sup></p>
 <p>This paragraph should not be part of the note, as it is not indented.</p>