code: function(el) {
      if (el == null) return false;
      if (el.start && el.end) {
        return el.start >= this.start && el.start <= this.end &&
               el.end   >= this.start && el.end   <= this.end;
      } else {
        return el >= this.start && el <= this.end;
      }
    }
docs: *
  @method contains(el)
  @returns Boolean
  @short Returns true if `el` is contained inside the range. `el` may be a
  value or another range.
  
  @example
  
  Number.range(5, 10).contains(7)         -> true
  Number.range(5, 10).contains(2)         -> false
  janToMay.contains(mar)                  -> true
  janToMay.contains(marToAug)             -> false
  janToMay.contains(febToApr)             -> true
  
  @param {RangeElement} el
  
  *