docs: function(to) {
              if (this.rectify()) {
                  if (this.canMerge(to)) {
                      var rowspan = this.idx_end.row - this.idx_start.row + 1,
                          colspan = this.idx_end.col - this.idx_start.col + 1;
  
                      for (var row = this.idx_start.row, maxr = this.idx_end.row; row <= maxr; row++) {
                          for (var col = this.idx_start.col, maxc = this.idx_end.col; col <= maxc; col++) {
  
                              if (row == this.idx_start.row && col == this.idx_start.col) {
                                  if (rowspan > 1) {
                                      this.map[row][col].el.setAttribute('rowspan', rowspan);
                                  }
                                  if (colspan > 1) {
                                      this.map[row][col].el.setAttribute('colspan', colspan);
                                  }
                              } else {
                                  // transfer content
                                  if (!(/^\s*<br\/?>\s*$/.test(this.map[row][col].el.innerHTML.toLowerCase()))) {
                                      this.map[this.idx_start.row][this.idx_start.col].el.innerHTML += ' ' + this.map[row][col].el.innerHTML;
                                  }
                                  removeElement(this.map[row][col].el);
                              }
                          }
                      }
                      this.rectify();
                  } else {
                      if (window.console) {
                          console.log('Do not know how to merge allready merged cells.');
                      }
                  }
              }
          }