Calculate / limit lines in textarea

I had to answer and interesting question on StackOverflow (SO): Can can you limit (well, first of all calculate, of course) the number of lines in a textarea?

How to add line breaks into a textarea

I use the textarea tag when I include code into my posts, but I wasn't able to figure out a way to add a line break in there as the <br/> tag would be displayed in a textarea instead of actually breaking the line. Well, as I could find out through the article Adding/Insert Line Breaks into a Textarea the key is to add this 'code' instead: &#13;

It's tiny but can be really annoying if you don't have the information. ;)