# MathML Support

The support for MathML in MathJax involves two functions: the first looks for `<math>` tags within your document and marks them for later processing by MathJax, and the second converts the MathML to the internal format used by MathJax, where one of MathJax’s output processors then displays it in the web page.

In addition, MathJax’s internal format is essentially MathML (with a few additions), implemented as javascript objects rather than DOM elements. MathJax’s various input processors all convert their original format into this internal MathML format, and its output processors take this MathML and produce the proper output from it. Because the internal format is MathML-based, MathJax provides the ability to convert to and from MathML notation.

Although some browsers have native support for rendering MathML, not all do, and so MathJax makes it possible to view MathML notation in all browsers. Even for those that do support MathML, it may be valuable to use MathJax, since that will produce consistent output across all browsers, and MathJax implements features and functionality that is not available in some native MathML implementations.

## MathML in HTML pages

For MathML that is handled via the preprocessor, you should not use named MathML entities, but rather use numeric entities like `&#x221A;` or unicode characters embedded in the page itself. The reason is that entities are replaced by the browser before MathJax runs, and some browsers report errors for unknown entities. For browsers that are not MathML-aware, that will cause errors to be displayed for the MathML entities. While that might not occur in the browser you are using to compose your pages, it can happen with other browsers, so you should avoid the named entities whenever possible. If you must use named entities, you may need to declare them in the DOCTYPE declaration by hand.

When you use MathML in an HTML document rather than an XHTML one (MathJax will work with both), you should not use the “self-closing” form for MathML tags with no content, but should use separate open and close tags. That is, use

    <mspace width="thinmathspace"></mspace>

rather than `<mspace width="thinmathspace" />`. This is because HTML does not have self-closing tags, and some browsers will get the nesting of tags wrong if you attempt to use them. For example, with `<mspace width="1em" />`, since there is no closing tag, the rest of the mathematics will become the content of the `<mspace>` tag; but since `<mspace>` should have no content, the rest of the mathematics will not be displayed. This is a common error that should be avoided. Modern browsers that support HTML5 should be able to handle self-closing tags, but older browsers have problems with them, so if you want your mathematics to be visible to the widest audience, do not use the self-closing form in HTML documents.

## Supported MathML tags

MathJax supports the MathML3.0 mathematics tags, with some limitations. The MathML support is still under active development, so some tags are not yet implemented, and some features are not fully developed, but are coming.

The deficiencies include:

- No support for alignment groups in tables.

- Not all attributes are supported for tables. E.g., `columnspan` and `rowspan` are not implemented yet.

- Experimental support for the elementary math tags: `mstack`, `mlongdiv`, `msgroup`, `msrow`, `mscarries`, and `mscarry` (via the `mml3` extension, see below).

- Experimental support for bidirectional mathematics (via the `mml3` extension, see below).

See the results of the MathML3.0 test suite for details.

## Content MathML

The version 2 `content-mathml` extension is not yet available in version 3.

## Experimental mml3 extension

MathML includes a number of tags that support elementary-school mathematics, like `<mstack>` and `<mlongdiv>`. MathJax has only experimental support for these tags via the mml3 extension. This uses an XSLT transform to convert these tags into other presentation MathML tags that MathJax has implemented. This does a reasonable job for some constructs, and a poorer job for others, but it does make it possible to process elementary math within MathJax. Better support is planned for the future.

To activate experimental features in your documents, simply include `[mml]/mml3` in the `load` array of the `loader` section of your configuration:

    MathJax = {
      loader: {load: ['[mml]/mml3']}
    };

This will install a pre-filter on the MathML input jax that performs the XSLT transform before processing it.

## Semantics and Annotations

Some popular annotation formats like TeX, Maple, or Content MathML are often included in the MathML source via the `semantics` element. This is particularly true of MathML that is generated by other software, such as editors or computational tools.

MathJax provides access to these annotations through the `"Show Math As"` menu, via the `Annotations` submenu. See the MathML Annotation Framework and the Contextual Menu Options documentation for details.