Re: [xsl] lookaheads in XSLT2 regexes

["Imsieke, Gerrit, le-tex" <gerrit.imsieke@xxxxxxxxx>]

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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