       // Require 10xx xxxx  10xx xxxx  1110 xxxx.
       if _slowPath(buffer & 0xc0c0f0 != 0x8080e0) {
         if buffer & 0x00c000 != 0x008000 { return (nil, 1) }
-        return (nil, 2) // Only return this if all checks on CU0 & CU1 passed.
+        return (nil, 2) // All checks on CU0 & CU1 passed.
       }
       // Extract data bits.
       let value = (buffer & 0x3f0000) >> 16

  ///   - length: The length of the code unit sequence in bytes if it is
  ///   well-formed; otherwise the *maximal subpart of the ill-formed
  ///   sequence* (Unicode 8.0.0, Ch 3.9, D93b), i.e. the number of leading
  ///   code units that were valid or 1 in case none were valid. Unicode
  ///   recommends to skip these bytes bytes and replace them by a single
  ///   replacement character (U+FFFD).
  ///

      // Consume the decoded bytes (or maximal subpart of ill-formed sequence).
      let bitsConsumed = 8 &* length
      _sanityCheck(1...4 ~= length && bitsConsumed <= _bitsInBuffer)
      // Swift doesn't allow shifts greater than or equal to the type width.
      // _decodeBuffer >>= UInt32(bitsConsumed) // >>= 32 crashes.
      _decodeBuffer = UInt32(truncatingBitPattern:
        UInt64(_decodeBuffer) >> (UInt64(bitsConsumed) & 0x1f))
      _bitsInBuffer = _bitsInBuffer &- bitsConsumed
