code: function stringify(start, end) {
    var values = []
    var positions = []
    var offsets = []
  
    add(start)
    add(end)
  
    if (positions.length !== 0) {
      values.push(positions.join('-'))
    }
  
    if (offsets.length !== 0) {
      values.push(offsets.join('-'))
    }
  
    return values.join(', ')
  
    // Add a position.
    function add(position) {
      var tuple = compile(position)
  
      if (tuple) {
        positions.push(tuple[0])
  
        if (tuple[1]) {
          offsets.push(tuple[1])
        }
      }
    }
  }
docs: Compile a location.