get() {
      return this._svg || shape.getSVG(true, shapeDOM => {
        for (const [attribute, value] of Object.entries(rootAttributes)) {
          shapeDOM.setAttribute(attribute, value);
        }
      });
    }
Add a single shape to a CSS sprite

@param {SVGShape} shape          Shape
@param {boolean} needsRegular    Needs a :regular pseudo class in CSS
@param {number} index            Index
@param {number} position         Position bits
@param {number} rootAttributes   Root element attributes
@param {number} positionX        Horizontal position within the sprite
@param {number} positionY        Vertical position within the sprite