Includes its body, if the user check validates.

----

!Usage

<wiki:UserCheck exists="true|false">
;:''JSP or HTML content''
</wiki:UserCheck>

!Parameters

;__exists__: If set to "true", then the content is included if there is a valid username; if set to "false", includes the content when there is no valid username.

!Example
{{{
    <wiki:UserCheck exists="true">
        G'day,<wiki:UserName />
    </wiki:UserCheck>

    <wiki:UserCheck exists="false">
        Set your name in <wiki:LinkTo page="UserPreferences">UserPreferences</wiki:LinkTo>
    </wiki:UserCheck>
}}}

Displays a greeting, if the user has validated; else displays a link to the page UserPreferences.