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[xsl] Initial whitespace in PI from XSLT, main body

2022-05-07 16:14:30
[Could not post whole thing due to size limitation on list. Complete text 
version and separate appendices are currently available at 
Since that is not a permanent store (hence the “temp/” in the path), I will 
post the appendices [A], [B], and [C], hopefully as a reply to this, shortly.]

I have discovered a discrepancy between Saxon[1] on the one hand and 
xsltproc[2] & my intuition on the other when it comes to writing a processing 
instruction whose string value starts with whitespace. E.g.
  <?syd   This is a test. This is only a test. ?>

When reading this PI, I fully expect the string value to start with the letter 
‘T’ and end with the string “t. ”. This makes sense because the XML spec,[3] in 
production 16, defines a PI as
  '<?' PITarget (S (Char* - (Char* '?>' Char*)))? '?>'
where, of course, 'S' is one or more occurrences of any of the four whitespace 
characters. While the value string is not really defined in the prose, it is 
clear from the production that the S is only required if there is a string. 
This implies that the purpose of the S is to separate the PITarget from the 
string.[4] I am used to greedy matching, so it makes sense to me that a parser 
would think of any and all whitespace immediately following the PITarget as a 
delimiter, and thus not return it as part of the value string.

I grant that, as far as my small brain can tell, it would not be against the 
production for a parser to use non-greedy matching, decide only the first 
whitespace character matches the S, and that all following whitespace 
characters should match "Char*". But that is not what I expect, because it 
seems to violate the spirit of the production — if that were the desired 
result, why wouldn’t the spec use "(#x20 | #x9 | #xD | #xA)" between the 
PITarget and the rest, rather than "(#x20 | #x9 | #xD | #xA)+"?[5] Furthermore, 
if this were the parsing algorithm, it would be possible to end up with a 
string value of a PI that contained nothing but whitespace characters. While 
not utterly insane, it does seem to be the kind of complication that is likely 
to be more trouble than it is worth. Besides, as I said, I am used to greedy 
matching and expect writers of XML parsers to be like me. 🙂

And, perhaps more importantly, the string value of a processing instruction 
node in the XDM is defined as “The data part of the source PI, not including 
the whitespace that separates it from the PITarget.”[6]

But what if I try to write a PI whose string value starts with one or more 
whitespace characters?

First, we know the processor is required to write out one or more whitespace 
characters between the PITarget and the value string. I presume (without 
knowing for sure) that the processor is welcome to use whatever set of 
whitespace characters it wants to separate the PITarget from the rest when it 
serializes a PI. (I have never seen nor heard of a processor that uses anything 
other than a single space (U+0020) character, myself.) I further suspect that 
most processors would choose to not use any whitespace characters when 
serializing a PI that does not have a value string.

But if I am explicitly giving the processor a string to use as the value of the 
PI that starts with space, I sort of expect that string, including the leading 
space, to appear in the output after whatever space the processor normally uses 
to separate a PITarget from a value string. And that is the behavior I get from 
 But it is not the behavior I get from 

So is Saxon in error, or is xsltproc in error, or is the spec ambiguous and 
either behavior is OK, or something else?

P.S. I have tried a few various combinations of the -strip: commandline 
parameter to Saxon, and changing the 
 from an XSLT 1.0 pgm to an XSLT 3.0 pgm, same results.

[1] SaxonJ-HE 11.2 run in GNU bash on an Ubuntu 20.04.4 system.
[2] Using libxml 20910, libxslt 10134 and libexslt 820 on same system.
[3] https://www.w3.org/TR/REC-xml/
[4] This becomes clearer if you reduce all that “any sequence of characters 
except NOT "?>"” stuff to something simple:
         '<?'  PITarget  (S (StringSansQuestionPointy) )?  '?>'
[5] I have to admit, though, the fact that the spec lists the illegal PITargets 
as “" XML ", " xml "”, putting spaces around the illegal Names, gives me pause. 
If there were only a space after, it would really boggle my thought process. 
But since there is space both before and after I suspect it is not intended, 
and this is just an error or editorial style I disagree with.
[6] Kay, Michael, _XSLT 2.0 and XPath 2.0_, 4th ed. Wiley Publishing, Inc., 
Indianapolis, IN. p. 51.

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