_saveInteractionStartData(e, newValue) {
      const progressBarDom = this.shadowRoot.querySelector(".ui5-slider-progress").getBoundingClientRect();
      // Save the state of the value properties on the start of the interaction
      this._startValueAtBeginningOfAction = this.startValue;
      this._endValueAtBeginningOfAction = this.endValue;
      // Save the initial press point coordinates (position)
      const ctor = this.constructor;
      this._initialPageXPosition = ctor.getPageXValueFromEvent(e);
      // Which element of the Range Slider is pressed and which value property to be modified on further interaction
      this._pressTargetAndAffectedValue(this._initialPageXPosition, newValue);
      // Use the progress bar to save the initial coordinates of the start-handle when the interaction begins.
      this._initialStartHandlePageX = this.directionStart === "left" ? progressBarDom.left : progressBarDom.right;
    }
Determines and saves needed values from the start of the interaction:

Is the value calculated is within the currently selected range;
Initial pageX position of the start handle affected by the interaction;
Initial pageX value of the pressed postion;
Affected value property by the action;

@private