SelectCheckboxMenu SelectManyCheckbox is used to choose multiple items displayed in an overlay.
      Selected Items
      Basic
      No cities selected
      Multiple
      No cities selected
      Grouped
      No cars selected
      <h:form>
          <h:panelGrid columns="2" cellpadding="5">
              <h:outputLabel for="menu" value="Basic:" />
              <p:selectCheckboxMenu id="menu" value="#{checkboxView.selectedCities}" label="Cities" 
                                    filter="true" filterMatchMode="startsWith" panelStyle="width:250px">
                  <f:selectItems value="#{checkboxView.cities}" />
              </p:selectCheckboxMenu>
      
              <h:outputLabel for="multiple" value="Multiple:" />
              <p:selectCheckboxMenu id="multiple" value="#{checkboxView.selectedCities2}" label="Cities" multiple="true" 
                                    filter="true" filterMatchMode="startsWith" panelStyle="width:250px">
                  <f:selectItems value="#{checkboxView.cities}" />
              </p:selectCheckboxMenu>
              
              <h:outputLabel for="grouped" value="Grouped:" />
              <p:selectCheckboxMenu id="grouped" value="#{checkboxView.selectedCars}" label="Cars" multiple="true" 
                                    filter="true" filterMatchMode="startsWith" panelStyle="width:250px">
                  <f:selectItems value="#{checkboxView.cars}" />
              </p:selectCheckboxMenu>
          </h:panelGrid>
      
          <p:commandButton value="Submit" update="displayItems" oncomplete="PF('itemDialog').show()" style="margin-top:10px;" />
      
          <p:dialog header="Selected Items" modal="true" showEffect="fade" hideEffect="fade" widgetVar="itemDialog" width="250">
              <p:outputPanel id="displayItems">
                  <p:dataList value="#{checkboxView.selectedCities}" var="city" emptyMessage="No cities selected" style="margin-bottom: 10px;">
                      <f:facet name="header">
                          Basic
                      </f:facet>
                      #{city}
                  </p:dataList>
      
                  <p:dataList value="#{checkboxView.selectedCities2}" var="city" emptyMessage="No cities selected">
                      <f:facet name="header">
                          Multiple
                      </f:facet>
                      #{city}
                  </p:dataList>
                  
                  <p:dataList value="#{checkboxView.selectedCars}" var="car" emptyMessage="No cars selected">
                      <f:facet name="header">
                          Grouped
                      </f:facet>
                      #{car}
                  </p:dataList>
              </p:outputPanel>
          </p:dialog>
      </h:form>
                      
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