public XSLFSheet appendContent(XSLFSheet src){
CTGroupShape spTree = getSpTree();
int numShapes = getShapeList().size();
CTGroupShape srcTree = src.getSpTree();
for(XmlObject ch : srcTree.selectPath("*")){
if(ch instanceof CTShape){ // simple shape
spTree.addNewSp().set(ch);
} else if (ch instanceof CTGroupShape){
spTree.addNewGrpSp().set(ch);
} else if (ch instanceof CTConnector){