primefaces - How can I not send form when press button inside form? -

i have primefaces form

<h:form id="profilegridform"> <h:panelgroup>                         <p:inplace id="myid" editor="#{bean.changelangenabled}">                             <h:selectonemenu value="#{bean.changedbillinglanguage}">                                 ...                             </h:selectonemenu>                         </p:inplace>                     </h:panelgroup>  <h:panelgroup>                         <p:commandbutton value="model" update="modelform" action="#{modelbean.clear}" ajax="true"                                          oncomplete="pf('showmodel').show()"/>                     </h:panelgroup>  </h:form> 

when press model button call changedbillinglanguage method. how can not send form when press button inside form?