Re: RFE: Invalid IDREF cause 'Copy as Reference' to silently fail

We now consider this bug to be fixed.

* When the "Copy As Reference" menu item is not disabled (grayed) and 
this command fails to create a reference, it now displays an error 
dialog box. The error message does not explain why the command has 
failed. Anyway this explanation would be quite technical and hard to 
understand for the average user.

* With option "Allow advanced use of XInclude" turned OFF and an XHTML5 
element having id="What?", the "Copy As Reference" menu item is now 
disabled (grayed). id="What?" is a valid XHTML5 ID but cannot be used to 
create an shorthand XPointer. A shorthand XPointer (AKA barename) must 
be an NCName.

* With option "Allow advanced use of XInclude" turned ON and an XHTML5 
element having id="What?", the "Copy As Reference" menu item works and 
creates an Element scheme XPointer looking like element(/1/2/2/3) or 
element(valid_ancestor_id/2/4/1), valid_ancestor_id being an NCName.



On 3/1/23 14:23, Leif H Silli wrote:
> Great to hear that we will get an error message - hope the message at 
> least will give the user a hint of why it failed.
> 
> I do not know enough about the thing that XInclude is built on 
> (XPointer) to know all the possibilities. However, libxml2 does not 
> support xpointer="What?". For instance, if you run the command
> 
> xmllint --xinclude foo.xhtml
> 
> on a document which references <div id="What?"/> by way of 
> xpointer="What?", then you get an error message and inclusion does not 
> take place. The XInclude spec also says that xpointer attribute does not 
> support percent escaping, so that is also not an option.
> 
> Thus, I suspect that in order to use XInclude to embed the 'What?' 
> fragment, you would have to find another XPointer method than the pure 
> and direct xpointer="What?". For instance, perhaps one would have to 
> rely on features of "Allow advanced use of XInclude" to circumwent the 
> problem.
> 
> Currently, with regard to advanced use of XInclude, if you run "Copy as 
> Reference", and XXE detects that there is a id="foo", then it gives 
> priority to using xpointer="foo". And this seems to be the case, also 
> when the id contains special characters such as id="foo?". But one 
> possible workaround could be to to make sure - when Advanced Include is 
> enabled - that "Copy as References" tries one of the advanced options if 
> the simple option fails.
> 
> Anyway, as long as it can be done in an interoperatable way, I agree 
> that it would be very cool if you can make 'Copy as Reference' work even 
> with an ID like 'What?'.
> 
> Leif
> 
> 
> Hussein Shafie on 2023-03-01 10:06:
>> The problem you report is a real one, but we don't completely agree
>> with your analysis:
>>
>> * <div id='What?'>Foo</div>
>>
>> id='What?' is just fine in an XHTML5 document, no matter whether XXE
>> supports XInclude or not.
>>
>> * Yes, 'Copy as Reference' should report an error message when it
>> fails to create a reference out of the selection.
>>
>> This bug is fixed now and 'Copy as Reference' will report an error
>> message in this case. However the error message will not give you much
>> details about what went wrong.
>>
>> * With <div>Foo</div> (no id attribute) selected
>>
>> 'Copy as Reference' works fine if
>> (1) this div is the root element of the document
>> and/or
>> (2) option "Allow advanced use of XInclude" is turned on. See
>> http://www.xmlmind.com/xmleditor/_distrib/doc/help/editOptions.html
>>
>> Otherwise 'Copy as Reference' is disabled (grayed menu entry "Edit →
>> Reference → Copy as Reference").
>>
>> Now, we'll have to investigate to see if we can (or is legit to) make
>> 'Copy as Reference' work even with an ID like 'What?'.
>>
>>
>> On 2/28/23 23:23, Leif H Silli wrote:
>>> For XHTML5, the XML-based validity constraints on id attributes (that 
>>> is, on IDREFs), have been lifted. And so, since XHTML5 lacks those 
>>> constraints, XXE does not prevent us from adding the following 
>>> element to an XHTML5 document:
>>>
>>>      <div id='What?' >Foo</div>
>>>
>>> Explanation: Questionmarks are amongst the “special characters” that 
>>> are not permitted inside id attributes of XHTML1.x documents – and 
>>> thus such characters would also not occur in id attributes, as long 
>>> as you were using a validating editor such as XXE. Hence, in the good 
>>> old days before XHTML5 was introduced, the issue I am taking up in 
>>> this message, would basically never occur.
>>>
>>> However, provided the XXE user makes use of XInclude inclusions, the 
>>> validity constraints of XHTML1.x are as relevant as ever before.
>>>
>>> And so, given the above fragment, if, using XXE, you select it, and 
>>> then select the command 'Copy as Reference' (from the bottom submenu 
>>> of the Edit menu), nothing happens. You do not get a warning telling 
>>> you that 'Copy as Reference' failed because the id attribute 
>>> contained characters which, from the XInclude point of view, are 
>>> forbidden. The only way to understand that it did not work, is when 
>>> you paste the reference - without getting any result.
>>>
>>> So basically, in the above example, currently we get the same 
>>> feedback as if we tried to apply 'Copy as Reference' to the following 
>>> element (which lacks an id attribute):
>>>
>>>      <div>Foo</div>
>>>
>>> That is: We  do not get any feedback.
>>>
>>> Proposal for a fix:
>>>
>>> EITHER, let XXE display a 'failure' message based on a validity 
>>> conformance check of the IDREF, every time 'Copy as Reference' is 
>>> used without success. (This requires the presence of an id attribute.)
>>>
>>> OR, let XXE simply display a general warning, every time 'Copy as 
>>> Reference' does not yield any result - even when the reason for the 
>>> “failure” is that the element lacks an id attribute.
>>>
>>> That is, in the case of the 'OR' option, if the user tries to apply 
>>> 'Copy as Reference' to an element which lacks the id attribute, 
>>> display the general warning. And also, display the same general 
>>> warning if the content of the id attribute fails to yield any result.
>>>
>>> Example text of general warning: “No reference was copied, either 
>>> because there was no id attribute, or (if there was an id attribute) 
>>> because the content of the id attribute of the selected element [or, 
>>> if running with the 'advanced' XInclude option, of nearest parent 
>>> element] did not meet the validity constraints required by XInclude.”
>>>
>>> I believe at least the 'OR' option should work also when XXE is 
>>> running with 'advanced XInclude' support enabled. In my case, I was 
>>> running XXE with the 'advanced' XInclude support active, when I 
>>> failed to get a result  when copying the child element of a fragment. 
>>> At first I thought the issue was specific to the advanced XInclude 
>>> support, but then I came to understand that the issue is so 
>>> fundamental that it is also present in XXE's default XInclude support 
>>> mode.
>>>
>>> Leif Halvard Silli


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