_calculateRangeOffset(currentPageXPos, initialStartHandlePageXPos) {
      // Return the current values if there is no difference in the
      // positions of the initial press and the current pointer
      if (this._initialPageXPosition === currentPageXPos) {
        return [this.startValue, this.endValue];
      }
      const min = this._effectiveMin;
      const max = this._effectiveMax;
      const selectedRange = this.endValue - this.startValue;
      // Computes the new value based on the difference of the current cursor location from the start of the interaction
      let startValue = this._calculateStartValueByOffset(currentPageXPos, initialStartHandlePageXPos);
      // When the end handle reaches the max possible value prevent the start handle from moving
      // And the opposite - if the start handle reaches the beginning of the slider keep the initially selected range.
      const ctor = this.constructor;
      startValue = ctor.clipValue(startValue, min, max - selectedRange);
      return [startValue, startValue + selectedRange];
    }
Calculates startValue/endValue properties when the whole range is moved.

Uses the change of the position of the start handle and adds the initially
selected range to it, to determine the whole range offset.

@param {Integer} currentPageXPos The current horizontal position of the cursor/touch
@param {Integer} initialStartHandlePageXPos The initial horizontal position of the start handle

@private