system/Typography/Typography.php
public function autoTypography(string $str, bool $reduce_linebreaks = false): string
	{
		if ($str === '')
		{
			return '';
		}

		// Standardize Newlines to make matching easier
		if (strpos($str, "\r") !== false)
		{
			$str = str_replace(["\r\n", "\r"], "\n", $str);
		}

		// Reduce line breaks.  If there are more than two consecutive linebreaks
		// we'll compress them down to a maximum of two since there's no benefit to more.
		if ($reduce_linebreaks === false)
		{
			$str = preg_replace("/\n\n+/", "\n\n", $str);
		}

		// HTML comment tags don't conform to patterns of normal tags, so pull them out separately, only if needed
		$html_comments = [];
		if (strpos($str, '<!--') !== false && preg_match_all('#(<!\-\-.*?\-\->)#s', $str, $matches))
		{
			for ($i = 0, $total = count($matches[0]); $i < $total; $i ++)
			{
				$html_comments[] = $matches[0][$i];
				$str             = str_replace($matches[0][$i], '{@HC' . $i . '}', $str);
			}
		}

		// match and yank <pre> tags if they exist.  It's cheaper to do this separately since most content will
		// not contain <pre> tags, and it keeps the PCRE patterns below simpler and faster
		if (strpos($str, '<pre') !== false)
		{
			$str = preg_replace_callback('#<pre.*?>.*?</pre>#si', [$this, 'protectCharacters'], $str);
		}

		// Convert quotes within tags to temporary markers.
		$str = preg_replace_callback('#<.+?>#si', [$this, 'protectCharacters'], $str);

		// Do the same with braces if necessary
		if ($this->protectBracedQuotes === false)
		{
			$str = preg_replace_callback('#\{.+?\}#si', [$this, 'protectCharacters'], $str);
		}

		// Convert "ignore" tags to temporary marker.  The parser splits out the string at every tag
		// it encounters.  Certain inline tags, like image tags, links, span tags, etc. will be
		// adversely affected if they are split out so we'll convert the opening bracket < temporarily to: {@TAG}
		$str = preg_replace('#<(/*)(' . $this->inlineElements . ')([ >])#i', '{@TAG}\\1\\2\\3', $str);

		/* Split the string at every tag. This expression creates an array with this prototype:
		 *
		 * 	[array]
		 * 	{
		 * 		[0] = <opening tag>
		 * 		[1] = Content...
		 * 		[2] = <closing tag>
		 * 		Etc...
		 * 	}
		 */
		$chunks = preg_split('/(<(?:[^<>]+(?:"[^"]*"|\'[^\']*\')?)+>)/', $str, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);

		// Build our finalized string.  We cycle through the array, skipping tags, and processing the contained text
		$str     = '';
		$process = true;

		for ($i = 0, $c = count($chunks) - 1; $i <= $c; $i ++)
		{
			// Are we dealing with a tag? If so, we'll skip the processing for this cycle.
			// Well also set the "process" flag which allows us to skip <pre> tags and a few other things.
			if (preg_match('#<(/*)(' . $this->blockElements . ').*?>#', $chunks[$i], $match))
			{
				if (preg_match('#' . $this->skipElements . '#', $match[2]))
				{
					$process = ($match[1] === '/');
				}

				if ($match[1] === '')
				{
					$this->lastBlockElement = $match[2];
				}

				$str .= $chunks[$i];
				continue;
			}

			if ($process === false)
			{
				$str .= $chunks[$i];
				continue;
			}

			//  Force a newline to make sure end tags get processed by _format_newlines()
			if ($i === $c)
			{
				$chunks[$i] .= "\n";
			}

			//  Convert Newlines into <p> and <br /> tags
			$str .= $this->formatNewLines($chunks[$i]);
		}

		// No opening block level tag? Add it if needed.
		if (! preg_match('/^\s*<(?:' . $this->blockElements . ')/i', $str))
		{
			$str = preg_replace('/^(.*?)<(' . $this->blockElements . ')/i', '<p>$1</p><$2', $str);
		}

		// Convert quotes, elipsis, em-dashes, non-breaking spaces, and ampersands
		$str = $this->formatCharacters($str);

		// restore HTML comments
		for ($i = 0, $total = count($html_comments); $i < $total; $i ++)
		{
			// remove surrounding paragraph tags, but only if there's an opening paragraph tag
			// otherwise HTML comments at the ends of paragraphs will have the closing tag removed
			// if '<p>{@HC1}' then replace <p>{@HC1}</p> with the comment, else replace only {@HC1} with the comment
			$str = preg_replace('#(?(?=<p>\{@HC' . $i . '\})<p>\{@HC' . $i . '\}(\s*</p>)|\{@HC' . $i . '\})#s', $html_comments[$i], $str);
		}

		// Final clean up
		$table = [
			// If the user submitted their own paragraph tags within the text
			// we will retain them instead of using our tags.
			'/(<p[^>*?]>)<p>/'                              => '$1', // <?php BBEdit syntax coloring bug fix
			// Reduce multiple instances of opening/closing paragraph tags to a single one
			'#(</p>)+#'                                     => '</p>',
			'/(<p>\W*<p>)+/'                                => '<p>',
			// Clean up stray paragraph tags that appear before block level elements
			'#<p></p><(' . $this->blockElements . ')#'      => '<$1',
			// Clean up stray non-breaking spaces preceeding block elements
			'#(&nbsp;\s*)+<(' . $this->blockElements . ')#' => '  <$2',
			// Replace the temporary markers we added earlier
			'/\{@TAG\}/'                                    => '<',
			'/\{@DQ\}/'                                     => '"',
			'/\{@SQ\}/'                                     => "'",
			'/\{@DD\}/'                                     => '--',
			'/\{@NBS\}/'                                    => '  ',
			// An unintended consequence of the _format_newlines function is that
			// some of the newlines get truncated, resulting in <p> tags
			// starting immediately after <block> tags on the same line.
			// This forces a newline after such occurrences, which looks much nicer.
			"/><p>\n/"                                      => ">\n<p>",
			// Similarly, there might be cases where a closing </block> will follow
			// a closing </p> tag, so we'll correct it by adding a newline in between
			'#</p></#'                                      => "</p>\n</",
		];

		// Do we need to reduce empty lines?
		if ($reduce_linebreaks === true)
		{
			$table['#<p>\n*</p>#'] = '';
		}
		else
		{
			// If we have empty paragraph tags we add a non-breaking space
			// otherwise most browsers won't treat them as true paragraphs
			$table['#<p></p>#'] = '<p>&nbsp;</p>';
		}

		return preg_replace(array_keys($table), $table, $str);
	}
public function autoTypography(string $str, bool $reduce_linebreaks = false): string
	{
		if ($str === '')
		{
			return '';
		}

		// Standardize Newlines to make matching easier
		if (strpos($str, "\r") !== false)
		{
			$str = str_replace(["\r\n", "\r"], "\n", $str);
		}

		// Reduce line breaks.  If there are more than two consecutive linebreaks
		// we'll compress them down to a maximum of two since there's no benefit to more.
		if ($reduce_linebreaks === false)
		{
			$str = preg_replace("/\n\n+/", "\n\n", $str);
		}

		// HTML comment tags don't conform to patterns of normal tags, so pull them out separately, only if needed
		$html_comments = [];
		if (strpos($str, '<!--') !== false && preg_match_all('#(<!\-\-.*?\-\->)#s', $str, $matches))
		{
			for ($i = 0, $total = count($matches[0]); $i < $total; $i ++)
			{
				$html_comments[] = $matches[0][$i];
				$str             = str_replace($matches[0][$i], '{@HC' . $i . '}', $str);
			}
		}

		// match and yank <pre> tags if they exist.  It's cheaper to do this separately since most content will
		// not contain <pre> tags, and it keeps the PCRE patterns below simpler and faster
		if (strpos($str, '<pre') !== false)
		{
			$str = preg_replace_callback('#<pre.*?>.*?</pre>#si', [$this, 'protectCharacters'], $str);
		}

		// Convert quotes within tags to temporary markers.
		$str = preg_replace_callback('#<.+?>#si', [$this, 'protectCharacters'], $str);

		// Do the same with braces if necessary
		if ($this->protectBracedQuotes === false)
		{
			$str = preg_replace_callback('#\{.+?\}#si', [$this, 'protectCharacters'], $str);
		}

		// Convert "ignore" tags to temporary marker.  The parser splits out the string at every tag
		// it encounters.  Certain inline tags, like image tags, links, span tags, etc. will be
		// adversely affected if they are split out so we'll convert the opening bracket < temporarily to: {@TAG}
		$str = preg_replace('#<(/*)(' . $this->inlineElements . ')([ >])#i', '{@TAG}\\1\\2\\3', $str);

		/* Split the string at every tag. This expression creates an array with this prototype:
		 *
		 * 	[array]
		 * 	{
		 * 		[0] = <opening tag>
		 * 		[1] = Content...
		 * 		[2] = <closing tag>
		 * 		Etc...
		 * 	}
		 */
		$chunks = preg_split('/(<(?:[^<>]+(?:"[^"]*"|\'[^\']*\')?)+>)/', $str, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);

		// Build our finalized string.  We cycle through the array, skipping tags, and processing the contained text
		$str     = '';
		$process = true;

		for ($i = 0, $c = count($chunks) - 1; $i <= $c; $i ++)
		{
			// Are we dealing with a tag? If so, we'll skip the processing for this cycle.
			// Well also set the "process" flag which allows us to skip <pre> tags and a few other things.
			if (preg_match('#<(/*)(' . $this->blockElements . ').*?>#', $chunks[$i], $match))
			{
				if (preg_match('#' . $this->skipElements . '#', $match[2]))
				{
					$process = ($match[1] === '/');
				}

				if ($match[1] === '')
				{
					$this->lastBlockElement = $match[2];
				}

				$str .= $chunks[$i];
				continue;
			}

			if ($process === false)
			{
				$str .= $chunks[$i];
				continue;
			}

			//  Force a newline to make sure end tags get processed by _format_newlines()
			if ($i === $c)
			{
				$chunks[$i] .= "\n";
			}

			//  Convert Newlines into <p> and <br /> tags
			$str .= $this->formatNewLines($chunks[$i]);
		}

		// No opening block level tag? Add it if needed.
		if (! preg_match('/^\s*<(?:' . $this->blockElements . ')/i', $str))
		{
			$str = preg_replace('/^(.*?)<(' . $this->blockElements . ')/i', '<p>$1</p><$2', $str);
		}

		// Convert quotes, elipsis, em-dashes, non-breaking spaces, and ampersands
		$str = $this->formatCharacters($str);

		// restore HTML comments
		for ($i = 0, $total = count($html_comments); $i < $total; $i ++)
		{
			// remove surrounding paragraph tags, but only if there's an opening paragraph tag
			// otherwise HTML comments at the ends of paragraphs will have the closing tag removed
			// if '<p>{@HC1}' then replace <p>{@HC1}</p> with the comment, else replace only {@HC1} with the comment
			$str = preg_replace('#(?(?=<p>\{@HC' . $i . '\})<p>\{@HC' . $i . '\}(\s*</p>)|\{@HC' . $i . '\})#s', $html_comments[$i], $str);
		}

		// Final clean up
		$table = [
			// If the user submitted their own paragraph tags within the text
			// we will retain them instead of using our tags.
			'/(<p[^>*?]>)<p>/'                              => '$1', // <?php BBEdit syntax coloring bug fix
			// Reduce multiple instances of opening/closing paragraph tags to a single one
			'#(</p>)+#'                                     => '</p>',
			'/(<p>\W*<p>)+/'                                => '<p>',
			// Clean up stray paragraph tags that appear before block level elements
			'#<p></p><(' . $this->blockElements . ')#'      => '<$1',
			// Clean up stray non-breaking spaces preceeding block elements
			'#(&nbsp;\s*)+<(' . $this->blockElements . ')#' => '  <$2',
			// Replace the temporary markers we added earlier
			'/\{@TAG\}/'                                    => '<',
			'/\{@DQ\}/'                                     => '"',
			'/\{@SQ\}/'                                     => "'",
			'/\{@DD\}/'                                     => '--',
			'/\{@NBS\}/'                                    => '  ',
			// An unintended consequence of the _format_newlines function is that
			// some of the newlines get truncated, resulting in <p> tags
			// starting immediately after <block> tags on the same line.
			// This forces a newline after such occurrences, which looks much nicer.
			"/><p>\n/"                                      => ">\n<p>",
			// Similarly, there might be cases where a closing </block> will follow
			// a closing </p> tag, so we'll correct it by adding a newline in between
			'#</p></#'                                      => "</p>\n</",
		];

		// Do we need to reduce empty lines?
		if ($reduce_linebreaks === true)
		{
			$table['#<p>\n*</p>#'] = '';
		}
		else
		{
			// If we have empty paragraph tags we add a non-breaking space
			// otherwise most browsers won't treat them as true paragraphs
			$table['#<p></p>#'] = '<p>&nbsp;</p>';
		}

		return preg_replace(array_keys($table), $table, $str);
	}
Auto Typography

This function converts text, making it typographically correct:
- Converts double spaces into paragraphs.
- Converts single line breaks into <br /> tags
- Converts single and double quotes into correctly facing curly quote entities.
- Converts three dots into ellipsis.
- Converts double dashes into em-dashes.
- Converts two spaces into entities

@param string  $str
@param boolean $reduce_linebreaks whether to reduce more then two consecutive newlines to two

@return string