-----Original Message----- From: Dave McAlpin [mailto:dave...@epokinc.com] Sent: Monday, June 30, 2003 3:59 PM To: 'Drummond Reed'; 'Wachob, Gabe'; xri-...@lists.oasis-open.org Subject: RE: [xri-editors] Xref escaping rules

Here's the proposed text around this issue if you're interested.

XRIs MUST use escaped encoding as described in [RFC2396]. XRIs also have additional escaping rules described below.

XRIs can contain nested URIs as cross-references (see section [TODO]). These nested URIs can contain characters that, if unescaped, would cause misinterpretation when parsing the enclosing XRI. Consider the following XRI.

xri:@example/(http://www.example.com?id=1)

The generic parsing algorithm described in [RFC2396] would separate the above XRI into the following components

scheme = xri authority = <undefined> path = @example/(http://www.example.com? query = id=1)

The desired separation is

scheme = xri authority = <undefined> path = @example/(http://www.example.com?id=1) query = <undefined>

To avoid this type of misinterpretation, a URI (including an XRI) must be escaped before it can be used as a cross-reference. In particular, it MUST be converted such that the percent "%" character is escaped as "%25", the question mark "?" character is escaped as "%3F" and the pound sign "#" is escaped as "%28".

The example above, then, would be correctly expressed as

xri:@example/(http://www.example.com%3Fid=1)

Cross-references may be nested to any depth. The above rule is applied to each nesting level. For example, if the above XRI was used as a cross-reference, the percent sign "%" would be escaped to "%25".

xri:@example1/( xri:@example/(http://www.example.com%253Fid=1))

Furthermore, parentheses "(" and ")" MUST be escaped if they appear in a URI but do not delimit an XRI cross-reference. If an XRI cross-reference is embedded within an enclosing cross-reference, the parentheses delimiting the inner cross-reference MAY be escaped, but this is NOT RECOMMENDED because it complicates comparison. For example

xri:@example1/( xri:@example/(http://www.example.com%253Fid=1))

is preferred to

xri:@example1/( xri:@example/%28http://www.example.com%253Fid=1%29)

although both are legal and equivalent.

Before a URI may be used as a cross-reference, then, the following steps MUST be performed in order:

1. Escape all percent "%" characters as "%25". 2. Escape all parentheses "(" and ")" that do not delimit XRI cross-references as "%28" and "%29", respectively. 3. Escape all pound "#" characters as "%23". 4. Escape all question mark "?" characters as "%3F".

Note that the URI is assumed to be in an "escaped" form appropriate to its scheme before the above rules are applied.

Before a cross-reference is evaluated it MUST first be unescaped. If a cross-reference is contained in an enclosing cross-reference, the enclosing cross-reference MUST be unescaped before the inner cross-reference is evaluated and unescaped.