If it's text, then it refers to one of these values...
/**
* Does all sorts of transformations and filtering.
*/
define('FORMAT_MOODLE', '0');
/**
* Plain HTML (with some tags stripped).
*/
define('FORMAT_HTML', '1');
/**
* Plain text (even tags are printed in full).
*/
define('FORMAT_PLAIN', '2');
/**
* Wiki-formatted text.
* Deprecated: left here just to note that '3' is not used (at the moment)
* and to catch any latent wiki-like text (which generates an error)
* @deprecated since 2005!
*/
define('FORMAT_WIKI', '3');
/**
* Markdown-formatted text http://daringfireball.net/projects/markdown/
*/
define('FORMAT_MARKDOWN', '4');