How can I add custom attribute in mxCell tag of mxgraph? I want to add value2="customValue
<mxGraphModel dx="872" dy="535" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="850" pageHeight="1100" background="#ffffff">
<root>
<mxCell id="0"/>
<mxCell id="1" parent="0"/>
<mxCell id="2" value="wfState_1" value2="customValue" style="strokeColor:red" vertex="1" parent="1">
<mxGeometry x="50" y="110" width="120" height="70" as="geometry"/>
</mxCell>
</root>
</mxGraphModel>
// the function is
this.createVertexTemplateEntry('rounded=0;whiteSpace=wrap;html=1;strokeColor=red;shadow=1', 120, 70, 'wfState_2', 'workFllow2', null, null, 'rect rectangle box'),