code: function(){
  		var extUL = (this.hasexcell>0);
  		var extDR = (this.hasexcell===2);
  		this.minbx = (!extUL ? 0 : -2);
  		this.minby = (!extUL ? 0 : -2);
  		this.maxbx = (!extDR ? 2*this.cols : 2*this.cols+2);
  		this.maxby = (!extDR ? 2*this.rows : 2*this.rows+2);
  
  		this.puzzle.cursor.setminmax();
  	}
docs: --------------------------------------------------------------------------- bd.setminmax()   盤面のbx,byの最小値/最大値をセットする ---------------------------------------------------------------------------