toString() {
    // Concatting to a string is faster than creating an array and then
    // .join()ing for small (<100KB) arrays.
    // https://jsperf.com/join-vs-loop-w-type-test
    let str = ''
    for (const elem of this.elems) {
      if (typeof elem.value === 'string') str += elem.value
    }
    return str
  }
Returns the content of the Text object as a simple string, ignoring any
non-character elements.