@Override
    public void add(final Widget widget) {
//        GWT.log("Adding widget " + widget.getClass().getName());

        if (widget instanceof HelpHTML) {
            addHelpHtml((HelpHTML) widget);
        } else if (widget instanceof DescriptionHTML) {
            addDescriptionHtml((DescriptionHTML) widget);
        } else {
            // Not a HelpHTML so must be the childWidget
            if (childWidget != null) {
                throw new IllegalStateException("FormGroup can only contain one child widget that is not a HelpHTML. " +
                                                "Class: " + widget.getClass().getName());
            }
            this.childWidget = widget;
            if (id != null) {
                widget.getElement().setId(id);
            }
            widget.addStyleName("allow-focus");
        }
        updateFormGroupPanel();
//
//        formGroupPanel.clear();
//        formGroupPanel.add(labelPanel);
//        formGroupPanel.add(descriptionPanel);
//        formGroupPanel.add(widget);
//        formGroupPanel.add(feedback);
    }
Plain text, any HTML will be escaped.
The helpText attr trumps the {@code <form:HelpHTML>} element.
<p>
To programmatically set HTML help text, use {@link FormGroup#overrideHelpText(SafeHtml)}.
</p>
stroom-core-client-widget/src/main/java/stroom/widget/form/client/FormGroup.java