How to close a modalPanel?

[vh]

In my modalPanel, I have a ok button. If the operation succeed, the ok button will close the modalPanel, if operation fail, I want to show error msg on the modalPanel and leave it open.
How do I control if to close the panel?

[ilya_shaikovsky]

for me - the next code works as you defined.

<ui:define name="body">
 <f:verbatim>
 <a
 href="javascript:Richfaces.showModalPanel('_panel',{left:'auto', top:'auto'})">Show
 Modal Panel</a>
 </f:verbatim>
 <rich:modalPanel id="_panel">
 <f:facet name="header">
 <h:outputText value="test"></h:outputText>
 </f:facet>
 <h:form id="mpform">
 <a4j:outputPanel ajaxRendered="true">
 <h:messages id="error"></h:messages>
 </a4j:outputPanel>
 <h:inputText value="#{bean.property}" required="true"></h:inputText>
 <a4j:commandLink value="click" oncomplete="windowclose();" reRender="test"/>
 </h:form>
 </rich:modalPanel>
 <script type="text/javascript">
//<![CDATA[
function windowclose(){
 if (document.getElementById('mpform:error')==null){
 Richfaces.hideModalPanel('_panel');
 };
};
 //]]>
</script>
 </ui:define>

My function just check if the messages appeared and depending on this condition closes the window or does nothing.