code: function setStartPoint() {
              if (!startPoint || !startPoint.tagName || (startPoint.tagName.toLowerCase() !== 'td' && startPoint.tagName.toLowerCase() !== 'th')) {
                  console.error('Impossible to identify start Cell point.', startPoint);
                  return;
              }
              _startPoint.colPos = startPoint.cellIndex;
              if (!startPoint.parentElement || !startPoint.parentElement.tagName || startPoint.parentElement.tagName.toLowerCase() !== 'tr') {
                  console.error('Impossible to identify start Row point.', startPoint);
                  return;
              }
              _startPoint.rowPos = startPoint.parentElement.rowIndex;
          }
docs: //////////////////////////////////////////// Private functions //////////////////////////////////////////// 
  Set the startPoint of action.