Displaying Special Characters In A <div>

I have a problem displaying a divbox containing a html-textarea -
everything works fine with "normal" characters. However, when the
textarea contains special chars like <P> or ' , the box fails to show:

function show(divbox)
{
divbox.style.display=''
}

<div id="divbox" style="display:none" >
<form action="action.php" method="post>
<textarea name ="txt">Text</textarea>
</form>
</div>

If the Text in the textarea is for instance
HERE IS A "QUOTE"

it works fine, while
HERE IS A 'QUOTE'
produces an error

<br>-tags works fine, but
<p>-tags doesn't