Setting the Initial Text of Liferay UI Input Editor

Include the below line at the top of the page to access the liferay-ui elements.

<%@ taglib uri="http://liferay.com/tld/ui" prefix="liferay-ui" %>

The below line adds the Text Editor to the page.

<liferay-ui:input-editor initmethod="initDefaultMessage" name="textEditor" ></liferay-ui:input-editor>

This code adds content that as soon as the editor is initialized.
Note the <portlet:namespace /> tag in the function name.

<script type="text/javascript">
function <portlet:namespace />initDefaultMessage() {
    return 'Text to test';
}
</script>