Well, technically it does not have to be on the same line as long as there is no character between the ending ">" from start tag and the starting "<" from the closing tag. That is you need to end with
...></textarea>
as in the example below:
<p><label>Comments:<br>
<textarea id = "comments" rows = "4" cols = "36"
placeholder = "Enter comments here"
class = "valid"></textarea>
</label>
</p>