<?xml version="1.0" encoding="utf-8"?>
<form>
    <fieldset name="custom">
        <field name="customhtml" type="editor" 
            label="COM_RSTBOX_TEXT" 
            description="COM_RSTBOX_TEXT_DESC"
            rows="5" 
            cols="40" 
            filter="raw"
            buttons="true"
            hiddenLabel="true"
        />
    </fieldset>
</form>