docs: function applyDefaultTextStyle(textStyle) {
      var opt = textStyle.insideRollbackOpt;
  
      // Only `insideRollbackOpt` created (in `setTextStyleCommon`),
      // applyDefaultTextStyle works.
      if (!opt || textStyle.textFill != null) {
          return;
      }
  
      var useInsideStyle = opt.useInsideStyle;
      var textPosition = textStyle.insideRawTextPosition;
      var insideRollback;
      var autoColor = opt.autoColor;
  
      if (useInsideStyle !== false
          && (useInsideStyle === true
              || (opt.isRectText
                  && textPosition
                  // textPosition can be [10, 30]
                  && typeof textPosition === 'string'
                  && textPosition.indexOf('inside') >= 0
              )
          )
      ) {
          insideRollback = {
              textFill: null,
              textStroke: textStyle.textStroke,
              textStrokeWidth: textStyle.textStrokeWidth
          };
          textStyle.textFill = '#fff';
          // Consider text with #fff overflow its container.
          if (textStyle.textStroke == null) {
              textStyle.textStroke = autoColor;
              textStyle.textStrokeWidth == null && (textStyle.textStrokeWidth = 2);
          }
      }
      else if (autoColor != null) {
          insideRollback = {textFill: null};
          textStyle.textFill = autoColor;
      }
  
      // Always set `insideRollback`, for clearing previous.
      if (insideRollback) {
          textStyle.insideRollback = insideRollback;
      }
  }