code: func decodeArgAppendNoPlus(dst, src []byte) []byte {
  	if bytes.IndexByte(src, '%') < 0 {
  		// fast path: src doesn't contain encoded chars
  		return append(dst, src...)
  	}
  
  	// slow path
  	for i := 0; i < len(src); i++ {
  		c := src[i]
  		if c == '%' {
  			if i+2 >= len(src) {
  				return append(dst, src[i:]...)
  			}
  			x2 := hex2intTable[src[i+2]]
  			x1 := hex2intTable[src[i+1]]
  			if x1 == 16 || x2 == 16 {
  				dst = append(dst, '%')
  			} else {
  				dst = append(dst, x1<<4|x2)
  				i += 2
  			}
  		} else {
  			dst = append(dst, c)
  		}
  	}
  	return dst
  }
docs: // decodeArgAppendNoPlus is almost identical to decodeArgAppend, but it doesn't
  // substitute '+' with ' '.
  //
  // The function is copy-pasted from decodeArgAppend due to the performance
  // reasons only.