var w = fw.selection[0].width;
var x = fw.selection[0].left;
var y = fw.selection[0].top;
var cols = prompt("分割数",3);
var mgn = prompt("マージン",10);
var colsW = (w-mgn*(cols-1))/cols;
var guideX = x;
for(var i=0;i<=cols;i++){
  fw.getDocumentDOM().addGuide(guideX, "vertical");
  if(i!==cols && i!==0){
    guideX+=mgn;
    fw.getDocumentDOM().addGuide(guideX, "vertical");
  }
  guideX += colsW;
};