[xslt] Close brace in literal terminates expression in attribute value template

[Phil Shafer <phil juniper net>]

What is the proper way to use a literal close brace within an
expression inside an attribute value template?

      <e a="{substring-before($v, '}')}"/>

The spec says:

  http://www.w3.org/TR/xslt#attribute-value-templates

    A right curly brace inside a Literal in an expression is not
    recognized as terminating the expression.

But this does not seem to be the case.  In the example below, a
substring-before() invocation using '{' works, but using '}' gives
an error.


    % cat /tmp/x.xsl
    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
    <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"; version="1.0">
      <xsl:variable name="v" select="&quot;before{during}after&quot;"/>
      <xsl:template match="/">
        <top>
          <e a="{substring-before($v, '{')}"/>
        </top>
      </xsl:template>
    </xsl:stylesheet>
    % echo '<in/>' | xsltproc /tmp/x.xsl -
    <?xml version="1.0"?>
    <top><e a="before"/></top>
    % sed "s/'{'/'}'/" /tmp/x.xsl > /tmp/y.xsl
    % cat /tmp/y.xsl
    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
    <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"; version="1.0">
      <xsl:variable name="v" select="&quot;before{during}after&quot;"/>
      <xsl:template match="/">
        <top>
          <e a="{substring-before($v, '}')}"/>
        </top>
      </xsl:template>
    </xsl:stylesheet>
    % echo '<in/>' | xsltproc /tmp/y.xsl -
    XPath error : Unfinished literal
    compilation error: file /tmp/y.xsl line 6 element e
    Attribute 'a': Failed to compile the expression 'substring-before($v, '' in the AVT.
    % 


The same section of the spec says:

    When an attribute value template is instantiated, a double left or
    right curly brace outside an expression will be replaced by a
    single curly brace. It is an error if a right curly brace occurs
    in an attribute value template outside an expression without being
    followed by a second right curly brace.

So using double braces ("}}") should not work, since the
doubling-as-escape only works outside expressions.  I tested it and
it also fails, since the expression is terminated on the first close
brace.

My take is that this is a bug in libxslt, but I'd like
confirmation before I start working up a fix.

Thanks,
 Phil