From Joomla! Documentation
The "API15" namespace is an archived namespace. This page contains information for a Joomla! version which is no longer supported. It exists only as a historical reference, it will not be improved and its content may be incomplete and/or contain broken links.
JDocumentRendererMessage is responsible for rendering the error stack. It is called whenever a
<jdoc:include type="message" /> statement is encountered in the document template.
|render||Renders the error stack and returns the results as a string|
jimport( 'joomla.document.html.renderer.message' );