RE: [xsl] lookaheads in XSLT2 regexes

I feel that \b is very much tied to a specific set of characters which might
not be exactly the set you want. I'd be more comfortable providing
general-purpose zero-width look-ahead and look-behind:

regex="(?<=\P{L})\p{{Lu}}{{2,}}(?=\P{L})"

which seems far more powerful.

Regards,

Michael Kay
http://www.saxonica.com/
http://twitter.com/michaelhkay

-----Original Message-----
From: Imsieke, Gerrit, le-tex 
[mailto:gerrit(_dot_)imsieke(_at_)le-tex(_dot_)de] 
Sent: 04 March 2010 17:12
To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Subject: Re: [xsl] lookaheads in XSLT2 regexes

Dear Liam,

Thanks for promoting the \b case. As an illustration for \b's 
usefulness, let me show how I tag acronyms for a recent project:

   <xsl:template match="text()" mode="majuscules">
     <xsl:analyze-string select="." 
regex="(^|[\p{{P}}\p{{Z}}\p{{C}}])(\p{{Lu}}{{2,}})([\p{{P}}\p{
{Z}}\p{{C}}]|$)">
       <xsl:matching-substring>
         <xsl:value-of select="regex-group(1)"/>
         <span class="majusc">
           <xsl:value-of select="regex-group(2)"/>
         </span>
         <xsl:value-of select="regex-group(3)"/>
       </xsl:matching-substring>
       <xsl:non-matching-substring>
         <xsl:value-of select="."/>
       </xsl:non-matching-substring>
     </xsl:analyze-string>
   </xsl:template>

With (a reasonably defined) \b, this could be simplified to

   <xsl:template match="text()" mode="majuscules">
     <xsl:analyze-string select="." regex="\b\p{{Lu}}{{2,}}\b">
       <xsl:matching-substring>
         <span class="majusc">
           <xsl:value-of select="."/>
         </span>
       </xsl:matching-substring>
       <xsl:non-matching-substring>
         <xsl:value-of select="."/>
       </xsl:non-matching-substring>
     </xsl:analyze-string>
   </xsl:template>

Please note that \b should not only match the \w/\W boundary, 
but also the beginning or end of the string (or line, when 
the 'm' flag is in force). Speaking of the 'm' flag, and in 
Michael's direction: I regard \b as much more useful than the 
'm' flag when processing XML.

Gerrit



On 04.03.2010 06:59, Liam R E Quin wrote:

On Wed, 2010-03-03 at 21:27 +0000, Michael Kay wrote:

On the subject of \b I'll note we do have \W and \w


So we do, I overlooked that. And we define it a little differently 
from
Perl:

[#x0000-#x10FFFF]-[\p{P}\p{Z}\p{C}]

So for example "+" is regarded as part of a word, while "-" isn't. 
Which strikes me as totally useless, to be honest.


I agree.

We could fix that for XPath 2.1 I think.  I'm not sure what

the most

useful fix would be, I admit.

The Perl definition of "alphanumeric" plus "_" would

probably work for

\w, if one took alphnumeric to mean Letters|Numbers,

\p{L}|\p{N}, and

is coincidentally closer to what you get in Perl if you do
     use locale;
and your locale is (say) en_UK.UTF8, as it's then the same as the 
POSIX fragment [[:alpha:][:digit:]_]

There are lots of things that could be added to regular

expressions;

but \b is hard to emulate, useful, and also we seem to have

a rather

odd \w.  If \w is there, I think \b was omitted by mistake.

 Or that

\w was included by mistake!

Liam


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Gerrit Imsieke
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