Why don't documents have the ending php tag?

I see that many components, controllers etc all start with <?php but not ending with ?>, why is that?

I know that this is not necessary. Necessarily the only opening tag.

Yes I know that as well, it's quite obvious since it all comes like that out of the box, but my question is why, and if this is docuemented somewhere?

:)

"For files that contain only PHP code, the closing tag ("?>") is never permitted. It is not required by PHP, and omitting it prevents the accidental injection of trailing white space into the response."

http://framework.zen…formatting.html