1. All Opera versions, IE4+, and Netscape up to version 6.0 support the original PLAINTEXT specification which did not accept a closing tag.
  2. Internet Explorer up to version 3, Netscape 6.1+ and all Mosaic versions provide for a closing tag. A closing tag would allow placement in regions other than the end of a HTML document.

Plain PLAINTEXT element, with nested B element (It should be fairly evident if parsing stops beyond the end tag):
filler text plaintext <b>NESTED BOLD ELEMENT</b>, character entity: &amp; plaintext</plaintext> filler text <hr> <br> </body> </html>