Update mathjax math engine to use code compatible with v2 and v3

doc/math_engine/mathjax.page

@@ -8,60 +8,13 @@ title: MathJax
 HTML pages. It allows for very fine-grained configuration, is widely used and works on all modern
 browsers.
 
-This engine marks up math formulas with HTML `<script type="math/tex">` tags that MathJax
-understands. The only other thing to do is to include the MathJax library itself on the HTML page.
+This engine marks up math formulas with the standard MathJax syntax of `\(...\)` for inline math and
+`\[...\]` for block math (works for both version 2.x and 3.x of MathJax). The only other thing to do
+is to include the MathJax library itself on the HTML page.
 
 Note that kramdown does *not* ship with the MathJax library and that therefore the "default"
 template does *not* include a link to it! The
 [MathJax documentation](http://docs.mathjax.org/en/latest/start.html) describes how to add a link
 to MathJax to your page.
 
-## Using KaTeX instead of MathJax
-
-To use [KaTeX](https://khan.github.io/KaTeX/) instead of MathJax, activate the MathJax engine in
-kramdown, include the KaTeX Javascript files in the HTML file and put the following script at the
-end of the HTML file (note that JQuery is used for some parts but it can probably be done without
-it):
-
-~~~ html
-<script>
-  $("script[type='math/tex']").replaceWith(function() {
-      var tex = $(this).text();
-      return katex.renderToString(tex, \{displayMode: false});
-  });
-
-  $("script[type='math/tex; mode=display']").replaceWith(function() {
-      var tex = $(this).html();
-      return katex.renderToString(tex.replace(/%.*/g, ''), \{displayMode: true});
-  });
-</script>
-~~~
-
-Note that including the KaTeX Javascript files and the above script is normally done using a
-template file (see the [template option](../options.html).
-
-See [this comment](https://github.com/gettalong/kramdown/issues/292#issuecomment-257770946) for more
-details.
-
-
-## Options
-
-The MathJax engine supports the following keys of the option
-['math_engine_opts'](../options.html#option-math-engine-opts):
-
-preview
-: Specifies whether a preview should be shown. It defaults to `false` but if set to `true`, a
-  preview with the LaTeX code itself is shown. If it is set to any value other than `false` or
-  `true`, that value is shown as the preview.
-
-preview_as_code
-: When `true`, wraps the LaTeX code in `code` / `pre > code` tags instead of `span` / `div` tags,
-  mirroring the structure of inline code / code blocks. This ensures the content is styled like
-  regular code and improves legibility in RSS readers, text browsers, etc.
-
-  To prevent styling issues after MathJax has loaded, consider adding
-  `.MathJax_Preview:empty { display:none }` to your CSS.
-
-  Defaults to `false` and only works if `preview` is `true`.
-
 [MathJax]: http://www.mathjax.org

lib/kramdown/converter/math_engine/mathjax.rb

@@ -16,41 +16,8 @@ module Kramdown::Converter::MathEngine
   module Mathjax
 
     def self.call(converter, el, opts)
-      type = el.options[:category]
-      text = (el.value =~ /<|&/ ? "% <![CDATA[\n#{el.value} %]]>" : el.value).dup
-      text.gsub!(/<\/?script>?/, '')
-
-      preview = preview_string(converter, el, opts).dup
-
-      attr = {type: "math/tex#{type == :block ? '; mode=display' : ''}"}
-      preview << if type == :block
-                   converter.format_as_block_html('script', attr, text, opts[:indent])
-                 else
-                   converter.format_as_span_html('script', attr, text)
-                 end
-    end
-
-    def self.preview_string(converter, el, opts)
-      preview = converter.options[:math_engine_opts][:preview]
-      return '' unless preview
-
-      preview = (preview == true ? converter.escape_html(el.value) : preview.to_s)
-
-      preview_as_code = converter.options[:math_engine_opts][:preview_as_code]
-
-      if el.options[:category] == :block
-        if preview_as_code
-          converter.format_as_block_html('pre', {'class' => 'MathJax_Preview'},
-                                         converter.format_as_span_html('code', {}, preview),
-                                         opts[:indent])
-        else
-          converter.format_as_block_html('div', {'class' => 'MathJax_Preview'}, preview,
-                                         opts[:indent])
-        end
-      else
-        converter.format_as_span_html(preview_as_code ? 'code' : 'span',
-                                      {'class' => 'MathJax_Preview'}, preview)
-      end
+      value = converter.escape_html(el.value)
+      el.options[:category] == :block ?  "\\[#{value}\\]\n" : "\\(#{value}\\)"
     end
 
   end

test/test_files.rb

@@ -219,14 +219,14 @@ def tidy_output(out)
       'test/testcases/block/16_toc/toc_exclude.html',      # bc of different attribute ordering
       'test/testcases/span/autolinks/url_links.html',      # bc of quot entity being converted to char
       'test/testcases/block/14_table/empty_tag_in_cell.html', # bc of tidy
-      'test/testcases/block/15_math/mathjax_preview.html', # bc of mathjax preview
-      'test/testcases/block/15_math/mathjax_preview_simple.html', # bc of mathjax preview
-      'test/testcases/block/15_math/mathjax_preview_as_code.html', # bc of mathjax preview
       'test/testcases/span/01_link/link_defs_with_ial.html', # bc of attribute ordering
       'test/testcases/span/05_html/mark_element.html', # bc of tidy
       'test/testcases/block/09_html/xml.html', # bc of tidy
       'test/testcases/span/05_html/xml.html', # bc of tidy
       'test/testcases/block/03_paragraph/standalone_image.html', # bc of standalone image
+      'test/testcases/block/15_math/normal.html', # bc of mathjax and HTML parser
+      'test/testcases/block/15_math/gh_128.html', # bc of mathjax and HTML parser
+      'test/testcases/span/04_footnote/backlink_inline.html', # bc of mathjax
     ].compact
     Dir[File.dirname(__FILE__) + '/testcases/**/*.html'].each do |html_file|
       next if EXCLUDE_HTML_KD_FILES.any? {|f| html_file =~ /#{f}$/ }

test/testcases/block/15_math/gh_128.html

@@ -1,2 +1 @@
-<script type="math/tex; mode=display">% <![CDATA[
-alert('a') alert('b<') %]]></script>
+\[&lt;script&gt;alert('a')&lt;/script&gt; &lt;script&gt;alert('b&lt;')&lt;/script&gt;\]

test/testcases/block/15_math/normal.html

@@ -1,29 +1,28 @@
 <p>This is a para.
-<script type="math/tex">\text{LaTeX} \lambda_5</script></p>
+\(\text{LaTeX} \lambda_5\)</p>
 
-<script type="math/tex; mode=display">\lambda_5 = \alpha + 4</script>
+\[\lambda_5 = \alpha + 4\]
 
-<p><script type="math/tex">\lambda_\alpha > 5</script>
+<p>\(\lambda_\alpha &gt; 5\)
 This is a para.</p>
 
-<script type="math/tex; mode=display">% <![CDATA[
-\begin{align*}
-&=5 \\
-&=6 \\
-\end{align*} %]]></script>
+\[\begin{align*}
+&amp;=5 \\
+&amp;=6 \\
+\end{align*}\]
 
-<script type="math/tex; mode=display">5+5</script>
+\[5+5\]
 
-<script type="math/tex; mode=display">5+5</script>
+\[5+5\]
 
-<script type="math/tex; mode=display">5+5</script>
+\[5+5\]
 
-<script type="math/tex; mode=display">5+5</script>
+\[5+5\]
 
 <pre><code>$$5+5$$
 </code></pre>
 
-<script type="math/tex; mode=display">5+5</script>
-<script type="math/tex; mode=display">5+5</script>
+\[5+5\]
+\[5+5\]
 
-<script type="math/tex; mode=display">|x| = 5</script>
+\[|x| = 5\]

test/testcases/span/04_footnote/backlink_inline.html

@@ -66,7 +66,7 @@ <h1 id="header">header <a href="#fnref:list" class="reversefootnote">&#8617;</a
     </li>
     <li id="fn:mathblock">
 
-      <script type="math/tex; mode=display">x + 2</script>
+\[x + 2\]
       <p><a href="#fnref:mathblock" class="reversefootnote">&#8617;</a></p>
     </li>
     <li id="fn:html">

test/testcases/span/math/normal.html

@@ -1,10 +1,10 @@
-<p>This is <script type="math/tex">\lambda_\alpha > 5</script> some math. With <script type="math/tex">1
-+ 1</script> new line characters in between.</p>
+<p>This is \(\lambda_\alpha &gt; 5\) some math. With \(1
++ 1\) new line characters in between.</p>
 
-<p><script type="math/tex">5+5</script> inline math, $5.00 $$no math$$</p>
+<p>\(5+5\) inline math, $5.00 $$no math$$</p>
 
 <p>$$5+5$$ inline math</p>
 
-<p><script type="math/tex">5+5</script></p>
+<p>\(5+5\)</p>
 
 <p>$$5+5$$</p>