set selector(selector) {
    if (selector === this.selectorText) return

    this.selectorText = selector

    const {renderer, renderable} = this

    if (!renderable || !renderer) return

    const hasChanged = renderer.setSelector(renderable, selector)

    // If selector setter is not implemented, rerender the rule.
    if (!hasChanged) {
      renderer.replaceRule(renderable, this)
    }
  }
Set selector string.
Attention: use this with caution. Most browsers didn't implement
selectorText setter, so this may result in rerendering of entire Style Sheet.