do {
                        #
                        # Split the text using the first $tag_match pattern found.
                        # Text before  pattern will be first in the array, text after
                        # pattern will be at the end, and between will be any catches made 
                        # by the pattern.
                        #
                        $parts = preg_split($block_tag_re, $text, 2,
                                                                PREG_SPLIT_DELIM_CAPTURE);

                        # If in Markdown span mode, add a empty-string span-level hash 
                        # after each newline to prevent triggering any block element.
                        if ($span) {
                                $void = $this->hashPart("", ':');
                                $newline = "$void\n";
                                $parts[0] = $void . str_replace("\n", $newline, $parts[0]) . $void;
                        }

                        $parsed .= $parts[0]; # Text before current tag.

                        # If end of $text has been reached. Stop loop.
                        if (count($parts) < 3) {
                                $text = "";
                                break;
                        }

                        $tag  = $parts[1]; # Tag to handle.
                        $text = $parts[2]; # Remaining text after current tag.
                        $tag_re = preg_quote($tag); # For use in a regular expression.

                        #
                        # Check for: Code span marker
                        #
                        if ($tag{0} == "`") {
                                # Find corresponding end marker.
                                $tag_re = preg_quote($tag);
                                if (preg_match('{^(?>.+?|\n(?!\n))*?(?<!`)'.$tag_re.'(?!`)}',
                                        $text, $matches))
                                {
                                        # End marker found: pass text unchanged until marker.
                                        $parsed .= $tag . $matches[0];
                                        $text = substr($text, strlen($matches[0]));
                                }
                                else {
                                        # Unmatched marker: just skip it.
                                        $parsed .= $tag;
                                }
                        }
                        #
                        # Check for: Indented code block.
                        #
                        else if ($tag{0} == "\n" || $tag{0} == " ") {
                                # Indented code block: pass it unchanged, will be handled
                                # later.
                                $parsed .= $tag;
                        }
                        #
                        # Check for: Fenced code block marker.
                        #
                        else if ($tag{0} == "~") {
                                # Fenced code block marker: find matching end marker.
                                $tag_re = preg_quote(trim($tag));
                                if (preg_match('{^(?>.*\n)+?'.$tag_re.' *\n}', $text,
                                        $matches))
                                {
                                        # End marker found: pass text unchanged until marker.
                                        $parsed .= $tag . $matches[0];
                                        $text = substr($text, strlen($matches[0]));
                                }
                                else {
                                        # No end marker: just skip it.
                                        $parsed .= $tag;
                                }
                        }
                        #
                        # Check for: Opening Block level tag or
                        #            Opening Context Block tag (like ins and del)
                        #               used as a block tag (tag is alone on it's line).
                        #
                        else if (preg_match('{^<(?:'.$this->block_tags_re.')\b}', $tag) ||
                                (       preg_match('{^<(?:'.$this->context_block_tags_re.')\b}', $tag) &&
                                        preg_match($newline_before_re, $parsed) &&
                                        preg_match($newline_after_re, $text)    )
                                )
                        {
                                # Need to parse tag and following text using the HTML parser.
                                list($block_text, $text) = 
                                        $this->_hashHTMLBlocks_inHTML($tag . $text, "hashBlock", true);
                                
                                # Make sure it stays outside of any paragraph by adding newlines.
                                $parsed .= "\n\n$block_text\n\n";
                        }
                        #
                        # Check for: Clean tag (like script, math)
                        #            HTML Comments, processing instructions.
                        #
                        else if (preg_match('{^<(?:'.$this->clean_tags_re.')\b}', $tag) ||
                                $tag{1} == '!' || $tag{1} == '?')
                        {
                                # Need to parse tag and following text using the HTML parser.
                                # (don't check for markdown attribute)
                                list($block_text, $text) = 
                                        $this->_hashHTMLBlocks_inHTML($tag . $text, "hashClean", false);

                                $parsed .= $block_text;
                        }
                        #
                        # Check for: Tag with same name as enclosing tag.
                        #
                        else if ($enclosing_tag_re !== '' &&
                                # Same name as enclosing tag.
                                preg_match('{^</?(?:'.$enclosing_tag_re.')\b}', $tag))
                        {
                                #
                                # Increase/decrease nested tag count.
                                #
                                if ($tag{1} == '/')                                             $depth--;
                                else if ($tag{strlen($tag)-2} != '/')   $depth++;

                                if ($depth < 0) {
                                        #
                                        # Going out of parent element. Clean up and break so we
                                        # return to the calling function.
                                        #
                                        $text = $tag . $text;
                                        break;
                                }
                                
                                $parsed .= $tag;
                        }
                        else {
                                $parsed .= $tag;
                        }
                } while ($depth >= 0);