         while index != utf8.endIndex {
             let u = utf8[index]
             switch u {
-            case 32, 9, 10, 13: // space, tab, NL, CR
+            case asciiSpace,
+                 asciiTab,
+                 asciiNewLine,
+                 asciiCarriageReturn: // space, tab, NL, CR
                 index = utf8.index(after: index)
                 lastIndex = index
-            case 35: // #
+            case asciiHash: // #
                 while index != utf8.endIndex {
                     // Skip until end of line
                     let c = utf8[index]
                     index = utf8.index(after: index)
-                    if c == 10 || c == 13 {
+                    if c == asciiNewLine || c == asciiCarriageReturn {
                         break
                     }
                 }

          } else {
            return nil // Hex escape must have at least 1 digit
          }
        case 97: // \a
          out.append(UInt8(7))
        case 98: // \b
          out.append(UInt8(8))
        case 102: // \f
          out.append(UInt8(12))
        case 110: // \n
          out.append(UInt8(10))
        case 114: // \r
          out.append(UInt8(13))
        case 116: // \t
          out.append(UInt8(9))
        case 118: // \v
          out.append(UInt8(11))
        case 39, 34, 63: // \'  \"  \?
          out.append(escaped)
        default:
          return nil // Unrecognized escape

        }
        let c = utf8[index]
        let negated: Bool
        if c == asciiMinus {
            negated = true
            index = utf8.index(after: index)
        } else {
            negated = false
        }
        let inf = [asciiLowerI, asciiLowerN, asciiLowerF]
        let infinity = [asciiLowerI, asciiLowerN, asciiLowerF, asciiLowerI,
                        asciiLowerN, asciiLowerI, asciiLowerT, asciiLowerY]
        if (skipOptionalKeyword(bytes: inf)
            || skipOptionalKeyword(bytes: infinity) {
            return negated ? -Float.infinity : Float.infinity
        }
        return nil
