- From: Julian Reschke <julian.reschke@gmx.de>
- Date: Thu, 22 Dec 2005 16:51:15 +0100
- To: webdav <w3c-dist-auth@w3.org>
Hi,
I'd like to understand where we stand regarding property value round
tripping. Proposed text was posted in BugZilla (see
<http://ietf.cse.ucsc.edu:8080/bugzilla/show_bug.cgi?id=10>), and as far
as I can tell, two questions were left and sent to the mailing list for
discussion?
1) We're trying to encourage servers to preserve namespace prefixes,
thus making it a SHOULD level requirement.
2) Is there any interest in comments being preserved?
Re 1): there was little feedback on that, expcet for Wilfredo who's
concerned that people may be reyling on XML serializers that throw out
that information. Do people think that therefore SHOULD is too strong,
or would we just have to live that some servers wouldn't be able to do
it (it's not a MUST, after all).
Re 2): I don't think we got any feedback on this. As XML parsers are not
required to pass on information from comments, I'm inclined to say: not
a SHOULD (thus leave it in the bag of optional things servers can always
do).
So please try to give feedback on these two questions, and on the
suggested text in BugZilla. Hopefully then it can make it into the next
draft.
Best regards,
Julian
-- cut --
4.4 Property Values
The value of a property is always a (well-formed) XML fragment.
XML has been chosen because it is a flexible, self-describing,
structured data format that supports rich schema definitions, and
because of its support for multiple character sets. XML's self-
describing nature allows any property's value to be extended by
adding new elements. Older clients will not break when they
encounter extensions because they will still have the data specified
in the original schema and MUST ignore elements they do not
understand.
XML's support for multiple character sets allows any human-readable
property to be encoded and read in a character set familiar to the
user. XML's support for multiple human languages, using the "xml:
lang" attribute, handles cases where the same character set is
employed by multiple human languages. Note that xml:lang scope is
recursive, so a xml:lang attribute on any element containing a
property name element applies to the property value unless it has
been overridden by a more locally scoped attribute. Note that a
property only has one value, in one language (or language MAY be left
undefined), not multiple values in different languages or a single
value in multiple languages.
A property is always presented with an XML element consisting of the
property name, called the "property name element".
The simplest example is an empty property, which is different from a
property that does not exist:
<title xmlns="http://www.example.com/ns/"></title>
The value of the property appears inside the property name element.
It may be any kind of well-formed XML content, including both text-
only and mixed content. In the latter case, servers MUST preserve
certain aspects of the content. Using the terminology from [REC-XML-
INFOSET], the following rules apply:
For the property name Element Information Item itself:
[namespace name],
[local name],
[attributes] named "xml:lang" or any such attribute in scope,
[children] of type element or character.
On all Element Information Items that are descendants of the property
name element:
[namespace name],
[local name],
[attributes] and
[children] of type element or character.
On Attribute Information Items:
[namespace name],
[local name] and
[normalized value].
On Character Information Items::
[character code].
Future revisions of this specification may also require to preserve
namespace prefixes for child elements of the property elements, thus
servers SHOULD preserve the [prefix] as well. [[preserve.more.xml:
Feedback if we should ask implementors to preserve more in the future
is appreciated (such as comments).]]
XML Infoset attributes not listed above MAY be preserved by the
server, but clients MUST NOT rely on them being preserved.
Also note that whitespace inside values is always significant, and
that servers MUST NOT support overriding this using the xml:space
attribute.
4.4.1 Example - Property with Mixed Content
Consider a dead property 'author' created by the client as follows:
<D:prop xml:lang='en' xmlns:D='DAV:'>
<x:author xmlns:x='http://example.com/ns'>
<x:name>Jane Doe</x:name>
<!-- Jane's contact info -->
<x:uri type='email' added='2005-11-26'
>mailto:jane.doe@example.com</x:uri>
<x:uri type='web' added='2005-11-27'
>http://www.example.com</x:uri>
<x:notes xmlns:h='http://www.w3.org/1999/xhtml'>
Jane has been working way <h:em>too</h:em> long on the
long-awaited revision of <![CDATA[<RFC2518>]]>.
</x:notes>
</x:author>
</D:prop>
When retrieving the property, a server may return:
<D:prop xmlns:D='DAV:'>
<author xmlns="http://example.com/ns"
xmlns:x="http://example.com/ns"
xml:lang="en">
<x:name>Jane Doe</x:name>
<x:uri added="2005-11-26" type="email"
>mailto:jane.doe@example.com</x:uri>
<x:uri added="2005-11-27" type="web"
>http://www.example.com</x:uri>
<x:notes xmlns:h="http://www.w3.org/1999/xhtml">
Jane has been working way <h:em>too</h:em> long on the
long-awaited revision of <RFC2518>.
</x:notes>
</author>
</D:prop>
Note:
o The [prefix] for the property name itself was not preserved, being
non-significant,
o attribute values have been rewritten with double quotes instead of
single quotes (quoting style is not significant), and attribute
order has not been preserved,
o the xml:lang attribute has been returned on the property name
element itself (it was in scope when the property was set, but the
exact position in the response is not considered significant as
long as it is in scope),
o the [prefix] has been preserved on the child element "notes",
o whitespace between tags has been preserved everywhere (but the
fact that CDATA escaping was used is irrelevant), and
o the comment item was stripped (as would have been a processing
instruction item).
Implementation note:
There are cases such as editing scenarios where clients may
require that XML content is preserved character-by-character (such
as attribute ordering or quoting style). In this case, clients
should consider using a text-only property value by escaping all
characters that have a special meaning in XML parsing.
Received on Thursday, 22 December 2005 15:53:30 UTC