CodeMirror: XML mode

## XML mode

<html style="color: green"> <!-- this is a comment --> <head> <title>HTML Example</title> </head> <body> The indentation tries to be <em>somewhat &quot;do what I mean&quot;</em>... but might not match your style. </body> </html>

The XML mode supports two configuration parameters:

`htmlMode (boolean)`
  This switches the mode to parse HTML instead of XML. This means attributes do not have to be quoted, and some elements (such as `br`) do not require a closing tag.
`alignCDATA (boolean)`
  Setting this to true will force the opening tag of CDATA blocks to not be indented.

MIME types defined: `application/xml`, `text/html`.