code: function canMerge (m1, m2) {
    return (
      m1.type === m2.type &&
      m1.href === m2.href &&
      m1.end >= m2.start
    )
  }
docs: canMerge(m1, m2) determines if two markups can be merged.
  
  @param {Object} m1
  @param {Object} m2
  @return {Boolean}