RE: Proposed changes to CD01

[Eran Hammer-Lahav <eran@hueniverse.com>]

Please review.

> * Clarify <Alias> definition to express that the element does NOT extend the subject of the XRD and is only used to describe the subject resource

Text now reads:

        This URI value provides an additional identifier for the resource described by the XRD.  This value
        MUST be an absolute URI.  The <Alias> element does not extend the subject of the XRD. It is only used
        to provide other identifiers the subject resource can also be identified by.

> * Add text to <Subject> to make its design restrictions more explicit

Added to the introduction:

    The XRD schema is optimized for describing a single resource identified with a URI, as reflected by the
    definition of the <Subject> element. This design does not limit the
    applicability of the XRD schema from describing other classes of resources. This can be accomplished by
    by defining new extension elements capable to identifying different subject types.

> * Focus link selection on 'rel' with 'type' as a useful hint.

New definition for 'type':

    This string value provides a hint as to what the media type of the linked resource should be.
    The value of this attribute MUST be of the form of a media
    type defined in <xref linkend="rfc2046" />.  The IANA media types registry can be
    found at <ulink url="http://www.iana.org/assignments/media-types/"; />.  Note that this is
    only a hint and does not override the media type declared by the linked resource itself (e.g.
    the HTTP Content-Type header of a HTTP response obtained by following the link).

And small changes to text about link selection:

    Link selection criteria is determined by the XRD consumer's needs, and is based on the presence, absence, or
    value of the <Link> element attributes or child elements.  The selection
    criteria is usually based on the value of the 'rel' attribute with the value
    of the 'type' attribute used as a hint (helping to determine if the linked
    resource uses a familiar media type).

    Selection based on multiple criteria can be handled by performing multiple selections. Each selection is
    assigned preference order based on the consumer's needs. The selection results are compared to determine
    the most desired set. For example, a consumer processing an XRD describing a article, is looking for
    links to resources about the author, and giving higher preference to HTML documents over plain text, will
    perform two selection rounds, one for links with the 'author' relation type and another for choosing the
    most appropriate link is more than one is found.

> * Replace text about ignoring links with unknown template syntax with instructions to follow the protocol-specific rules on handling bad templates

New Text:

    The 'template' attribute provides a URI template which can be used to obtain the URI
    of the linked resource. Templates provide a mechanism for URI construction, taking a
    list of variables as input, and producing a URI string as an output.  The template
    syntax and vocabulary are determined by the application through which the XRD document
    is obtained and processed, and MAY be specific to the link relation type indicated
    by the 'rel' attribute of the corresponding <Link> element.  Applications utilizing the
    template mechanism must define the template syntax and processing rules (including
    error handling) as well as the variable vocabulary.

EHL