[html] Add a linebreak in an HTML text area

In a text area, as in the form input, then just a normal line break will work:

<textarea>
This is a text area
line breaks are automatic
</textarea>

If you're talking about normal text on the page, the <br /> (or just <br> if using plain 'ole HTML4) is a line break.

However, I'd say that you often don't actually want a line break. Usually, your text is seperated into paragraphs:

<p>
  This is some text
</p>
<p>
  This is some more
</p>

Which is much better because it gives a clue as to how your text is structured to machines that read it. Machines that read it include screen readers for the partially sighted or blind, seperating text into paragraphs gives it a chance of being presented correctly to these users.