The <xmp> element was used to surround HTML example text that should be rendered without interpreting any HTML elements between the opening and closing <xmp> tags. The element was deprecated in HTML 3.2 and is now obsolete.
The <plaintext> element was used to render HTML code as plain text. Since everything after the opening tag was rendered as plain text, there was no closing <plaintext> tag. This element is obsolete and should not be used. Instead, use the <code> or <pre> elements.