File: Source_URL_keyword_20080906.txt

It is proposed to register the following new text keyword for
use in PNG files:

Source URL

            If the image was produced by rendering a single
            URL the text portion of this chunk contains
            a URL identifying that web page, as defined
            by [http://tools.ietf.org/html/rfc3986#section-1.1.3|
            RFC 3986 section 1.1.3]