[relax-ng] Issue: long string literals

[James Clark <jjc@jclark.com>]

With the "pattern" parameter for XSD, it's possible that users may need to 
specify string literals that are very long. However, at the moment the 
compact syntax provides no way to format such literals nicely by breaking 
them over multiple lines nor to insert comments within such literals.

One possibility would be to provide a syntax for string literal 
concatenation, and allow a concatenation expression wherever a string 
literal is allowed, e.g.

# XSLT attribute value template
avt.datatype =
  xsd:token {
    pattern = "("
              + "[^\{\}]"  # anything other than a brace
              + "|\{\{"    # quoted opening brace
              + "|\}\}"    # quoted closing brace
              + "|\{([^""'\{\}]|""[^""]*""|'[^']*')+\}"  # an expression in 
braces
              + ")*"
  }

"+" as above is open possibility for string concatenation, but that 
requires some parsing lookahead to distinguish it from "+" meaning one or 
more.  Another possibility would be "." as in Perl.

Is this worth the extra complexity?

James