PHP Markdown Extra with support for jsMath
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drdrang Stop htmlifying special characters in math spans and blocks.
I don't understand why I was filtering the equation text through
htmlspecialchars in the first place--obviously the wrong thing to do.
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License.text Initial commit of PHP Markdown Extra 1.2.4 with no math additions. Dec 17, 2009
PHP Markdown Extra Readme.text

PHP Markdown Extra Math is an extension of Michel Fortin's PHP Markdown Extra, a PHP script for converting text written in Markdown to HTML. The extension consist of adding support for mathematical equations written in LaTeX to be processed by either the MathJax (default) or jsMath math rendering libraries.


Here's how it works. The author, writing in Markdown, inserts inline equations like this

where \(\alpha = (t_1 - t_0)/L\) is the rate at which the thickness increases

enclosing the math in a \( … \) pair, just as if writing in LaTeX. PHP Markdown Extra Math converts that to

where <span class="MathJax_Preview">[math]</span><script type="math/tex"> \alpha = (t_1 - t_0)/L </script> is the rate at which the thickness increases

for MathJax, or

where <span class="math"> \alpha = (t_1 - t_0)/L </span> is the rate at which the thickness increases

for jsMath. This is then converted by whichever math rendering library is being used to

inline math example

(The example is shown as an image but will be rendered as selectable and scalable text if the server has MathJax or jsMath installed.)

Similarly, display Math is enclosed in \[ … \] like this:

Putting this into Castigliano's equation, we get

\[\Delta = \frac{\partial U^*}{\partial F} = \frac{12F}{Eb} \int_0^L \frac{x^2}{(t_0 + \alpha x)^3} dx\]

which PHP Markdown Extra Math will turn into this HTML

<p>Putting this into the Castigliano equation, we get</p>

<span class="MathJax_Preview">[math]</span><script type="math/tex; mode=display">\Delta = \frac{\partial U^*}{\partial F} = \frac{12F}{Eb} \int_0^L \frac{x^2}{(t_0 + \alpha x)^3} dx</script>

for MathJax, or

<p>Putting this into the Castigliano equation, we get</p>

<div class="math">\Delta = \frac{\partial U^*}{\partial F} = \frac{12F}{Eb} \int_0^L \frac{x^2}{(t_0 + \alpha x)^3} dx</div>

for jsMath. This will be rendered as:

display math example


The choice of MathJax or jsMath output is made on Line 42 of markdown.php:

@define( 'MARKDOWN_MATH_TYPE',      "mathjax" );

Change the "mathjax" to "jsmath" to change the rendering library.

A MathJax detail

The <span class="MathJax_Preview">[…]</span> that precedes the MathJax code serves three purposes:

  1. It's a placeholder that's displayed briefly while the equations are rendered.
  2. It eliminates a rendering problem associated with Internet Explorer 8.
  3. It gives Instapaper users a sense of what the rendered equation would be (if they understand LaTeX).


PHP Markdown Extra Math is licensed under the same terms as PHP Markdown Extra. See the License.text file.