', '\#', '\+', '\-', '\.', '\!');
			foreach ($escape_sequences as $index => $escape_sequence)
			{
				if (strpos($text, $escape_sequence) !== FALSE)
				{
					$code = "\x1A".'\\'.$index.';';
					$text = str_replace($escape_sequence, $code, $text);
					$escape_sequence_map[$code] = $escape_sequence;
				}
			}
		}

		# ~

		$text = preg_replace('/\n\s*\n/', "\n\n", $text);
		$text = trim($text, "\n");
		$lines = explode("\n", $text);
		$text = parse_block_elements($lines);

		# decodes escape sequences
		if (!empty($escape_sequence_map)){
			foreach ($escape_sequence_map as $code => $escape_sequence)
			{
				$text = str_replace($code, $escape_sequence[1], $text);
			}
		}

		$text = rtrim($text, "\n");
		return $text;
	}

	function parse_block_elements(array $lines, $context = '')
	{
		$elements = array();
		$element = array('type' => '',);

		foreach ($lines as $line)
		{
			# markup (open)
			if ($element['type'] === 'markup' and ! isset($element['closed']))
			{
				if (preg_match('{<'.$element['subtype'].'>$}', $line)) # opening tag
				{
					$element['depth']++;
				}

				if (preg_match('{$}', $line)) # closing tag
				{
					$element['depth'] > 0
						? $element['depth']--
						: $element['closed'] = true;
				}
				$element['text'] .= "\n".$line;
				continue;
			}

			# *

			if ($line === '')
			{
				$element['interrupted'] = true;
				continue;
			}

			# blockquote (existing)
			if ($element['type'] === 'blockquote' and ! isset($element['interrupted']))
			{
				$line = preg_replace('/^[ ]*>[ ]?/', '', $line);
				$element['lines'] []= $line;
				continue;
			}

			# list (existing)
			if ($element['type'] === 'li')
			{
				if (preg_match('/^([ ]{0,3})(\d+[.]|[*+-])[ ](.*)/', $line, $matches))
				{
					if ($element['indentation'] !== $matches[1])
					{
						$element['lines'] []= $line;
					}
					else
					{
						unset($element['last']);
						$elements []= $element;
						$element = array(
							'type' => 'li',
							'indentation' => $matches[1],
							'last' => true,
							'lines' => array(
								preg_replace('/^[ ]{0,4}/', '', $matches[3]),
							),
						);
					}
					continue;
				}

				if (isset($element['interrupted']))
				{
					if ($line[0] === ' ')
					{
						$element['lines'] []= '';
						$line = preg_replace('/^[ ]{0,4}/', '', $line);
						$element['lines'] []= $line;
						continue;
					}
				}
				else
				{
					$line = preg_replace('/^[ ]{0,4}/', '', $line);
					$element['lines'] []= $line;
					continue;
				}
			}

			# paragraph
			if ($line[0] >= 'a' or $line[0] >= 'A' and $line[0] <= 'Z')
			{
				goto paragraph;
			}

			# code block
			if ($line[0] === ' ' and preg_match('/^[ ]{4}(.*)/', $line, $matches))
			{
				if (trim($line) === ''){continue;}
				if ($element['type'] === 'code')
				{
					if (isset($element['interrupted']))
					{
						$element['text'] .= "\n";
						unset ($element['interrupted']);
					}
					$element['text'] .= "\n".$matches[1];
				}
				else
				{
					$elements []= $element;
					$element = array(
						'type' => 'code',
						'text' => $matches[1],
					);
				}
				continue;
			}

			# setext heading (---)

			if ($line[0] === '-' and $element['type'] === 'p' and ! isset($element['interrupted']) and preg_match('/^[-]+[ ]*$/', $line))
			{
				$element['type'] = 'h.';
				$element['level'] = 2;
				continue;
			}

			# atx heading (#)

			if ($line[0] === '#' and preg_match('/^(#{1,6})[ ]*(.+?)[ ]*#*$/', $line, $matches))
			{
				$elements []= $element;
				$level = strlen($matches[1]);
				$element = array(
					'type' => 'h.',
					'text' => $matches[2],
					'level' => $level,
				);
				continue;
			}

			# setext heading (===)
			if ($line[0] === '=' and $element['type'] === 'p' and ! isset($element['interrupted']) and preg_match('/^[=]+[ ]*$/', $line))
			{
				$element['type'] = 'h.';
				$element['level'] = 1;
				continue;
			}

			$deindented_line = $line[0] !== ' ' ? $line : ltrim($line);
			if ($deindented_line === ''){continue;}

			# reference
			if ($deindented_line[0] === '[' and preg_match('/^\[(.+?)\]:[ ]*([^ ]+)/', $deindented_line, $matches))
			{
				$label = strtolower($matches[1]);
				$url = trim($matches[2], '<>');
				$reference_map[$label] = $url;
				continue;
			}

			# blockquote
			if ($deindented_line[0] === '>' and preg_match('/^>[ ]?(.*)/', $deindented_line, $matches))
			{
				if ($element['type'] === 'blockquote')
				{
					if (isset($element['interrupted']))
					{
						$element['lines'] []= '';
						unset($element['interrupted']);
					}
					$element['lines'] []= $matches[1];
				}
				else
				{
					$elements []= $element;
					$element = array(
						'type' => 'blockquote',
						'lines' => array(
							$matches[1],
						),
					);
				}
				continue;
			}

			# markup

			if ($deindented_line[0] === '<')
			{
				# self-closing tag
				if (preg_match('{^<.+?/>$}', $deindented_line))
				{
					$elements []= $element;
					$element = array(
						'type' => '',
						'text' => $deindented_line,
					);
					continue;
				}

				# opening tag
				if (preg_match('{^<(\w+)(?:[ ].*?)?>}', $deindented_line, $matches))
				{
					$elements []= $element;
					$element = array(
						'type' => 'markup',
						'subtype' => strtolower($matches[1]),
						'text' => $deindented_line,
						'depth' => 0,
					);
					preg_match('{\s*$}', $deindented_line) and $element['closed'] = true;
					continue;
				}
			}

			# horizontal rule
			if (preg_match('/^([-*_])([ ]{0,2}\1){2,}[ ]*$/', $deindented_line))
			{
				$elements []= $element;
				$element = array('type' => 'hr',);
				continue;
			}

			# list item
			if (preg_match('/^([ ]*)(\d+[.]|[*+-])[ ](.*)/', $line, $matches))
			{
				$elements []= $element;
				$element = array(
					'type' => 'li',
					'ordered' => isset($matches[2][1]),
					'indentation' => $matches[1],
					'last' => true,
					'lines' => array(
						preg_replace('/^[ ]{0,4}/', '', $matches[3]),
					),
				);
				continue;
			}

			paragraph:
			if ($element['type'] === 'p')
			{
				if (isset($element['interrupted']))
				{
					$elements []= $element;
					$element['text'] = $line;
					unset($element['interrupted']);
				}
				else {$element['text'] .= "\n".$line;}
			}
			else
			{
				$elements []= $element;
				$element = array(
					'type' => 'p',
					'text' => $line,
				);
			}
		}

		$elements []= $element;
		array_shift($elements);

		
		$markup = '';
		foreach ($elements as $index => $element)
		{
			switch ($element['type'])
			{
				case 'p':
					$text = parse_span_elements($element['text']);
					$text = preg_replace('/[ ]{2}\n/', '
'."\n", $text);
					if ($context === 'li' and $index === 0)
					{
						if (isset($element['interrupted']))	{	$markup .= "\n".'
'.$text.'
'."\n";}
						else {$markup .= $text;}
					}
					else{$markup .= '
'.$text.'
'."\n";}
					break;

				case 'blockquote':
					$text =parse_block_elements($element['lines']);
					$markup .= '
'."\n".$text.'
'."\n";
					break;

				case 'code':
					$text = htmlentities($element['text'], ENT_NOQUOTES);
					strpos($text, "\x1A\\") !== FALSE and $text = strtr($text, $escape_sequence_map);
					$markup .= '
'.$text.'
'."\n";
					break;

				case 'h.':
					$text = parse_span_elements($element['text']);
					$markup .= ''.$text.''."\n";
					break;

				case 'hr':
					$markup .= '
'."\n";
					break;

				case 'li':
					if (isset($element['ordered'])) # first
					{
						$list_type = $element['ordered'] ? 'ol' : 'ul';
						$markup .= '<'.$list_type.'>'."\n";
					}
					if (isset($element['interrupted']) and ! isset($element['last']))
					{
						$element['lines'] []= '';
					}
					$text = parse_block_elements($element['lines'], 'li');
					$markup .= '
'.$text.'
'."\n";
					isset($element['last']) and $markup .= ''."\n";
					break;

				default:
					$markup .= $element['text']."\n";
			}
		}
		return $markup;
	}

	function parse_span_elements($text)
	{
		$map = array();
		$index = 0;

		# code span
		if (strpos($text, '`') !== FALSE and preg_match_all('/`(.+?)`/', $text, $matches, PREG_SET_ORDER))
		{
			foreach ($matches as $matches)
			{
				$element_text = $matches[1];
				$element_text = htmlentities($element_text, ENT_NOQUOTES);

				# decodes escape sequences
				$escape_sequence_map
					and strpos($element_text, "\x1A") !== FALSE
					and $element_text = strtr($element_text, $escape_sequence_map);

				# composes element
				$element = ''.$element_text.'';

				# encodes element
				$code = "\x1A".'$'.$index;
				$text = str_replace($matches[0], $code, $text);
				$map[$code] = $element;
				$index ++;
			}
		}

		# inline link or image

		if (strpos($text, '](') !== FALSE and preg_match_all('/(!?)(\[((?:[^\[\]]|(?2))*)\])\((.*?)\)/', $text, $matches, PREG_SET_ORDER)) # inline
		{
			foreach ($matches as $matches)
			{
				$url = $matches[4];
				strpos($url, '&') !== FALSE and $url = preg_replace('/&(?!#?\w+;)/', '&', $url);
				if ($matches[1]) # image
				{
					$element = '';
				}
				else
				{
					$element_text =parse_span_elements($matches[3]);
					$element = ''.$element_text.'';
				}

	
				$code = "\x1A".'$'.$index;
				$text = str_replace($matches[0], $code, $text);
				$map[$code] = $element;
				$index ++;
			}
		}

		# reference link or image
		if (strpos($text, '[') !== FALSE and preg_match_all('/(!?)\[(.+?)\](?:\n?[ ]?\[(.*?)\])?/ms', $text, $matches, PREG_SET_ORDER))
		{
			foreach ($matches as $matches)
			{
				$link_definition = isset($matches[3]) && $matches[3]
					? $matches[3]
					: $matches[2]; # implicit

				$link_definition = strtolower($link_definition);
				if (isset($reference_map[$link_definition]))
				{
					$url = $reference_map[$link_definition];
					strpos($url, '&') !== FALSE and $url = preg_replace('/&(?!#?\w+;)/', '&', $url);
					if ($matches[1]) # image
					{
						$element = '';
					}
					else # anchor
					{
						$element_text = parse_span_elements($matches[2]);
						$element = ''.$element_text.'';
					}

					
					$code = "\x1A".'$'.$index;
					$text = str_replace($matches[0], $code, $text);
					$map[$code] = $element;
					$index ++;
				}
			}
		}

		# automatic link

		if (strpos($text, '<') !== FALSE and preg_match_all('/<((https?|ftp|dict):[^\^\s]+?)>/i', $text, $matches, PREG_SET_ORDER))
		{
			foreach ($matches as $matches)
			{
				$url = $matches[1];
				strpos($url, '&') !== FALSE and $url = preg_replace('/&(?!#?\w+;)/', '&', $url);
				$element = ':text';
				$element = str_replace(':text', $url, $element);
				$element = str_replace(':href', $url, $element);
				
				$code = "\x1A".'$'.$index;
				$text = str_replace($matches[0], $code, $text);
				$map[$code] = $element;
				$index ++;
			}
		}

		
		strpos($text, '&') !== FALSE and $text = preg_replace('/&(?!#?\w+;)/', '&', $text);
		strpos($text, '<') !== FALSE and $text = preg_replace('/<(?!\/?\w.*?>)/', '<', $text);

		if (strpos($text, '_') !== FALSE)
		{
			$text = preg_replace('/__(?=\S)(.+?)(?<=\S)__(?!_)/s', '$1', $text);
			$text = preg_replace('/_(?=\S)(.+?)(?<=\S)_/s', '$1', $text);
		}

		if (strpos($text, '*') !== FALSE)
		{
			$text = preg_replace('/\*\*(?=\S)(.+?)(?<=\S)\*\*(?!\*)/s', '$1', $text);
			$text = preg_replace('/\*(?=\S)(.+?)(?<=\S)\*/s', '$1', $text);
		}

		$text = strtr($text, $map);
		return $text;
	}
?>