Hard to extend due to html_str concatenation

The tool's javascript is written in an very old style. It uses string concatenation to form DOMStrings, which makes it not extensible at all.

For example, special characters can't be handled unless completely rewriting of all the related code.
I tried to do that and, unfortunately, something broke there. I found the codes coupling with each other heavily, making it hard to troubleshoot.

BTW, the repository seems not under maintenance any more (am I wrong?). I wonder if someone's going to refine it for better extensibility.