markRegionN = function (start) {
    let index = start || 0
    const length = this.string.length
    let region = length

    while (index < length - 1 && region === length) {
      if (this.hasVowelAtIndex(index) && !this.hasVowelAtIndex(index + 1)) {
        region = index + 2
      }
      index++
    }

    return region
  }
Marks a region after the first non-vowel following a vowel, or the
null region at the end of the word if there is no such non-vowel.

@param {Object} token Token to stem.
@param {Number} start Start index (defaults to 0).
@param {Number}       Region start index.