public static function valid($str)
	{
		// Cached expected number of octets after the current octet
		// until the beginning of the next UTF8 character sequence
		$mState = 0;

		// Cached Unicode character
		$mUcs4 = 0;

		// Cached expected number of octets in the current sequence
		$mBytes = 1;

		$len = strlen($str);

		for ($i = 0; $i < $len; $i++)
		{
			$in = ord($str{$i});

			if ($mState == 0)
			{
				// When mState is zero we expect either a US-ASCII character or a
				// multi-octet sequence.
				if (0 == (0x80 & ($in)))
				{
					// US-ASCII, pass straight through.
					$mBytes = 1;
				}
				elseif (0xC0 == (0xE0 & ($in)))
				{
					// First octet of 2 octet sequence
					$mUcs4 = ($in);
					$mUcs4 = ($mUcs4 & 0x1F) << 6;
					$mState = 1;
					$mBytes = 2;
				}
				elseif (0xE0 == (0xF0 & ($in)))
				{
					// First octet of 3 octet sequence
					$mUcs4 = ($in);
					$mUcs4 = ($mUcs4 & 0x0F) << 12;
					$mState = 2;
					$mBytes = 3;
				}
				elseif (0xF0 == (0xF8 & ($in)))
				{
					// First octet of 4 octet sequence
					$mUcs4 = ($in);
					$mUcs4 = ($mUcs4 & 0x07) << 18;
					$mState = 3;
					$mBytes = 4;
				}
				elseif (0xF8 == (0xFC & ($in)))
				{
					// First octet of 5 octet sequence.
					//
					// This is illegal because the encoded codepoint must be either
					// (a) not the shortest form or
					// (b) outside the Unicode range of 0-0x10FFFF.
					// Rather than trying to resynchronize, we will carry on until the end
					// of the sequence and let the later error handling code catch it.
					$mUcs4 = ($in);
					$mUcs4 = ($mUcs4 & 0x03) << 24;
					$mState = 4;
					$mBytes = 5;
				}
				elseif (0xFC == (0xFE & ($in)))
				{
					// First octet of 6 octet sequence, see comments for 5 octet sequence.
					$mUcs4 = ($in);
					$mUcs4 = ($mUcs4 & 1) << 30;
					$mState = 5;
					$mBytes = 6;
				}
				else
				{
					// Current octet is neither in the US-ASCII range nor a legal first
					// octet of a multi-octet sequence.
					return false;
				}
			}
			else
			{
				// When mState is non-zero, we expect a continuation of the multi-octet
				// sequence
				if (0x80 == (0xC0 & ($in)))
				{
					// Legal continuation.
					$shift = ($mState - 1) * 6;
					$tmp = $in;
					$tmp = ($tmp & 0x0000003F) << $shift;
					$mUcs4 |= $tmp;

					// End of the multi-octet sequence. mUcs4 now contains the final
					// Unicode codepoint to be output
					if (0 == --$mState)
					{
						// Check for illegal sequences and codepoints.
						// From Unicode 3.1, non-shortest form is illegal
						if (((2 == $mBytes) && ($mUcs4 < 0x0080)) || ((3 == $mBytes) && ($mUcs4 < 0x0800)) || ((4 == $mBytes) && ($mUcs4 < 0x10000))
							|| (4 < $mBytes)
							|| (($mUcs4 & 0xFFFFF800) == 0xD800) // From Unicode 3.2, surrogate characters are illegal
							|| ($mUcs4 > 0x10FFFF)) // Codepoints outside the Unicode range are illegal
						{
							return false;
						}

						// Initialize UTF8 cache.
						$mState = 0;
						$mUcs4 = 0;
						$mBytes = 1;
					}
				}
				else
				{
					//((0xC0 & (*in) != 0x80) && (mState != 0))
					// Incomplete multi-octet sequence.
					return false;
				}
			}
		}

		return true;
	}