How To Append (Or Other Method) a Lot of HTML Code?

I need to append a lot of HTML code. To improve readability, I don't want to write that all in one line, but split them as regular HTML. That would be like 15 new-lines or something. The problem is that JavaScript doesn't allow me to do that.

var target = $('.post .comment_this[rel="' + comment_id + '"]').parent().parent();

target.append('
    <div class="replies">
        <p>...</p>
        <img src="" alt="" />
    </div>
');

Basically, I need to add HTML in that place.

I need to add some variables too.