Markdown_Parser::doItalicsAndBold PHP Method

    function doItalicsAndBold($text)
    {
        $token_stack = array('');
        $text_stack = array('');
        $em = '';
        $strong = '';
        $tree_char_em = false;
        while (1) {
            #
            # Get prepared regular expression for seraching emphasis tokens
            # in current context.
            #
            $token_re = $this->em_strong_prepared_relist["{$em}{$strong}"];
            #
            # Each loop iteration seach for the next emphasis token.
            # Each token is then passed to handleSpanToken.
            #
            $parts = preg_split($token_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);
            $text_stack[0] .= $parts[0];
            $token =& $parts[1];
            $text =& $parts[2];
            if (empty($token)) {
                # Reached end of text span: empty stack without emitting.
                # any more emphasis.
                while ($token_stack[0]) {
                    $text_stack[1] .= array_shift($token_stack);
                    $text_stack[0] .= array_shift($text_stack);
                }
                break;
            }
            $token_len = strlen($token);
            if ($tree_char_em) {
                # Reached closing marker while inside a three-char emphasis.
                if ($token_len == 3) {
                    # Three-char closing marker, close em and strong.
                    array_shift($token_stack);
                    $span = array_shift($text_stack);
                    $span = $this->runSpanGamut($span);
                    $span = "<strong><em>{$span}</em></strong>";
                    $text_stack[0] .= $this->hashPart($span);
                    $em = '';
                    $strong = '';
                } else {
                    # Other closing marker: close one em or strong and
                    # change current token state to match the other
                    $token_stack[0] = str_repeat($token[0], 3 - $token_len);
                    $tag = $token_len == 2 ? "strong" : "em";
                    $span = $text_stack[0];
                    $span = $this->runSpanGamut($span);
                    $span = "<{$tag}>{$span}</{$tag}>";
                    $text_stack[0] = $this->hashPart($span);
                    ${$tag} = '';
                    # $$tag stands for $em or $strong
                }
                $tree_char_em = false;
            } else {
                if ($token_len == 3) {
                    if ($em) {
                        # Reached closing marker for both em and strong.
                        # Closing strong marker:
                        for ($i = 0; $i < 2; ++$i) {
                            $shifted_token = array_shift($token_stack);
                            $tag = strlen($shifted_token) == 2 ? "strong" : "em";
                            $span = array_shift($text_stack);
                            $span = $this->runSpanGamut($span);
                            $span = "<{$tag}>{$span}</{$tag}>";
                            $text_stack[0] .= $this->hashPart($span);
                            ${$tag} = '';
                            # $$tag stands for $em or $strong
                        }
                    } else {
                        # Reached opening three-char emphasis marker. Push on token
                        # stack; will be handled by the special condition above.
                        $em = $token[0];
                        $strong = "{$em}{$em}";
                        array_unshift($token_stack, $token);
                        array_unshift($text_stack, '');
                        $tree_char_em = true;
                    }
                } else {
                    if ($token_len == 2) {
                        if ($strong) {
                            # Unwind any dangling emphasis marker:
                            if (strlen($token_stack[0]) == 1) {
                                $text_stack[1] .= array_shift($token_stack);
                                $text_stack[0] .= array_shift($text_stack);
                            }
                            # Closing strong marker:
                            array_shift($token_stack);
                            $span = array_shift($text_stack);
                            $span = $this->runSpanGamut($span);
                            $span = "<strong>{$span}</strong>";
                            $text_stack[0] .= $this->hashPart($span);
                            $strong = '';
                        } else {
                            array_unshift($token_stack, $token);
                            array_unshift($text_stack, '');
                            $strong = $token;
                        }
                    } else {
                        # Here $token_len == 1
                        if ($em) {
                            if (strlen($token_stack[0]) == 1) {
                                # Closing emphasis marker:
                                array_shift($token_stack);
                                $span = array_shift($text_stack);
                                $span = $this->runSpanGamut($span);
                                $span = "<em>{$span}</em>";
                                $text_stack[0] .= $this->hashPart($span);
                                $em = '';
                            } else {
                                $text_stack[0] .= $token;
                            }
                        } else {
                            array_unshift($token_stack, $token);
                            array_unshift($text_stack, '');
                            $em = $token;
                        }
                    }
                }
            }
        }
        return $text_stack[0];
    }