[Expat-discuss] Fwd: I need help with error message 'xml declaration not at start of external en
Steve Fogoros
sfogoros at hsc.unt.edu
Tue Jun 24 20:12:13 CEST 2008
Nick,
Thank you for taking the time to help me work this out. I think in doing this kind of work, it's the nature of the beast to 'read what I want to see ...', and I am applying due diligence rather than have you do my work for me.
I misinterpreted the quotes on production [23] as a formal declaration that between the ' and the < at the beginning of '<?xml' there can be no other characters. While this is in fact true, it doesn't mean what I thought it meant in terms of no white space before XMLDoc. It is simply the system literal of the start of the XMLDoc declaration (as you said).
I agree the BNF rules should be all that is needed, but I find it is inconsistent with the Recommendation's descriptions regarding whitespace. In example, production [39] element ::= EmptyElemTag | STag content ETag, and production [40] STag ::= '<' Name (S Attribute)* S? '>', formally do not allow white space to exist as markup, yet, the Recommendation's descriptions on white space as markup within the document clearly allow and seem to encourage it (Section 2.10). Would it be true to say that current parsers that allow white space as markup within the document are not compliant with the recommendation since the BNF rule prohibits it?
I've also found where the recommendation clearly states that "Each XML document has one entity called the document entity, which serves as the starting point for the XML processor and may contain the whole document." (Section 4), Section 2.4 describes white space as allowed at the top level of the document entity and specifically outside the document element (production [1]).
I haven't found any description that specifically prohibits white space prior to XMLDoc.
I trust I'm reading this correctly?
And, so I am clear about why I am looking this close at the spec, we (UNT Health Science Center, Academic Information Services) are implementing application handling of XML data and ran into the issue of white space prior to XMLDoc failing the application. I can fix the application or the XML Parser, but which one I fix depends on which one is broken. So before I start changing the application, I want to make sure it isn't the XML Parser. But from what I'm finding in the recommendation, I think the parser needs to be fixed, or the recommendation should be more concise. I can go either way.
Steve Fogoros
>>> "Nick MacDonald" <nickmacd at gmail.com> 6/24/2008 9:46 AM >>>
Steve:
Careful to be sure you're reading what I wrote, and not what you want
to see... the Backus*Naur Form rules in the current XML spec are very
clear that whitespace is NOT ALLOWED where you wish they were.
http://www.w3.org/TR/2006/REC-xml-20060816/
http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form
The only rules you need to read are right here:
2.1 Well-Formed XML Documents
[Definition: A textual object is a well-formed XML document if:]
1.Taken as a whole, it matches the production labeled document.
2. It meets all the well-formedness constraints given in this specification.
3. Each of the parsed entities which is referenced directly or
indirectly within the document is well-formed.
Document
[1] document ::= prolog element Misc*
[3] S ::= (#x20 | #x9 | #xD | #xA)+
[22] prolog ::= XMLDecl? Misc* (doctypedecl Misc*)?
[23] XMLDecl ::= '<?xml' VersionInfo EncodingDecl?
SDDecl? S? '?>'
[24] VersionInfo ::= S 'version' Eq ("'" VersionNum "'" | '"'
VersionNum '"')
[25] Eq ::= S? '=' S?
[26] VersionNum ::= '1.0'
[27] Misc ::= Comment | PI | S
What you'd be looking for is a way to get some S (3) into the front of
a valid expansion of document (1). I can't see any way where this can
happen. The text elsewhere in the document is not really specifically
applicable to your case... there is certainly nothing more normative
than the explict BNF grammar provided, so you have to follow its
rules. You're confused by single quotes in the BNF? Just assume
they're double quotes if that's less confusing... the expectation is
that they are literal strings showing the exact characters you would
need to supply at that point in the grammar.
Nothing is wrong with eXpat... it is acting exactly as the spec dictates.
Nick
On Mon, Jun 23, 2008 at 11:30 AM, Steve Fogoros <sfogoros at hsc.unt.edu> wrote:
> I thought that too based on sections 2.1 and 2.8 of Extensible Markup
> Language (XML) 1.0 (Second Edition) at
> http://www.w3.org/TR/2000/REC-xml-20001006#NT-document . I was having
> trouble with the single quotes around the XMLDecl declaration. I've
> never seen that in a formal grammar and didn't want to assume it meant
> that nothing comes before the prolog, if it exists.
>
> I looked more closely and found section 2.4 of the specification does
> address my question and I believe states that whitespace is allowed
> before the XML specification:
>
> Quoted from URL referenced above:
>
> Text consists of intermingled character data and markup. [Definition:
> Markup takes the form of start-tags, end-tags, empty-element tags,
> entity references, character references, comments, CDATA section
> delimiters, document type declarations, processing instructions, XML
> declarations, text declarations, and any white space that is at the top
> level of the document entity (that is, outside the document element and
> not inside any other markup).]
> Nick, do you read this the same way I do? And, in case I haven't
> researched completely, has it been superceded in version 1.1?
>
> Thanks again for validating my assumptions. I think I will pass this on
> to the maintainers of expat
> Steve Fogoros
>
>>>> "Nick MacDonald" <nickmacd at gmail.com> 6/23/2008 7:52 AM >>>
> Perhaps you're not reading the same XML spec I am, because to me it is
> ABSOLUTELY clear that whitespace is not allowed to come before the XML
> specification:
>
> The primary rule states this:
>
> document ::= prolog element Misc*
>
> Note that a prolog is defined as so:
>
> prolog ::= XMLDecl? Misc* (doctypedecl Misc*)?
>
> Which says the XMLDecl is optional, but if present, it would be defined
> as so:
>
> XMLDecl ::= '<?xml' VersionInfo EncodingDecl? SDDecl? S? '?>'
>
> and since whitespace (the term 'S' as used in this ruleset) does not
> appear to be mentioned until the end of the XMLDecl, it makes it
> pretty clear its not allowed at the beginning.
>
> If you don't like this behaviour, you'd be better off lobbying the W3C
> to change the spec, but as it stands, eXpat is quite clearly enforcing
> the rules of validity for an XML document.
>
> Note that the rules also make it quite clear that you don't HAVE to
> have a XMLDecl, and thus without it your document can have as much
> initial whitespace as makes you happy... (I have tested this with
> eXpat and it works fully as expected.)
>
> Nick
>
>
> On Fri, Jun 20, 2008 at 1:02 PM, Steve Fogoros <sfogoros at hsc.unt.edu>
> wrote:
>> I'm using the PHP module XML Parser under PHP version 4.4.0.
>>
>> I get the referenced error due to new lines before the preamble.
>>
>> I've searched the error message and reviewed the w3c spec for
>> information on xml parsing. I haven't found anything that explicitly
>> states what a parser should do about leading white space outside of
> the
>> xml document. I've also noted that there are many failures of this
> type
>> reported on WordPress and RSS feed forums. In all cases, the
> correction
>> seems to be altering the provider application to submit the xml
> document
>> without any leading characters before the preamble.
>>
>> My question is: does the xml spec explicitly specify that there be
>> nothing other than the preamble at the beginning of a well formed
> xml
>> doc? Is this something that shoud/could be addressed in the parser
> (it
>> sure would eliminate a lot of failed implementations)?
>
> --
> Nick MacDonald
> NickMacD at gmail.com
>
>
>
>
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--
Nick MacDonald
NickMacD at gmail.com
--
Nick MacDonald
NickMacD at gmail.com
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