URIs, including URLs, will ideally be transmitted though protocols which accept them and data formats which define a context for them. However, in practice nowadays there are many occasions when URLs are included in plain ASCII non-marked-up text such as electronic mail and usenet news messages.
In this case, it is convenient to have a separate wrapper syntax to define delimiters which will enable the human or automated reader to recognize that the URI is a URI.
The recommendation is that the angle brackets (less than and greater than signs) of the ASCII set be used for this purpose.
These wrappers do not form part of the URL, are not mandatory, and should not be used in contexts (such as SGML parameters, HTTP requests, etc) in which delimiters are already specified.
Yes, Jim, I found it under <ftp://info.cern.ch/pub/www/doc> but you can probably pick it up from <ftp://ds.internic.net/rfc>.