[relax-ng] John Cowan's regex for RNG proposal, version 0.3

[John Cowan <jcowan@reutershealth.com>]

This is John Cowan's proposal 0.3 for regular expressions in RELAX NG.
It introduces one new pattern type, regex, which contains child elements
from the following set.  A regex pattern matches the sequence of what
its children match.  Here are the possible kinds of child elements:

0.  A regex element, either directly or via a ref element or an
externalRef element (which allows sub-regexes to be defined as named patterns).:
matches whatever its children match.  This serves the function of the
group element in ordinary pattern matching.

1.  A choice element: matches whatever any of its children match.

2.  A zeroOrMore element: matches zero or more instances of whatever its
children match.

3.  A oneOrMore element: matches one or more instances of whatever its
children match.

4.  An optional element: matches zero or one instance of whatever its
children match.

5.  An element that specifies n-to-m matching.  The syntax of this
depends on what, if anything, is added to RNG pattern matching.

6.  A choice element: matches anything that any of its children match.

7.  A submatch element (with mandatory id attribute): matches whatever
its children match.

8.  A submatchRef element (with mandatory id attribute): matches whatever
the submatch element with corresponding id has matched (the submatch must
come entirely before any corresponding submatchRef).

9.  A caseFolded element: matches whatever its children match after
all Unicode letters in both the children and the corresponding matched
content has been case-folded.

10.  An anchor element (with mandatory type argument, one of "bos", "eos",
"bol", "eol"): matches nothing, but must be at the beginning of the string,
the end of the string, the beginning of a line, or the end of a line.

11.  A value element: matches the sequence of characters specified by its
character content.

12.  A collection element: matches a single character belonging to the
specified collection.  The children of a collection element specify
the members of the collection, and can be any of the following:

	A.  Another collection element: specifies what its children specify.

	B.  A charSet element: specifies the characters which constitute
	its character content.

	C.  A charRange element: specifies the characters which appear in
	Unicode order between the first and second character (inclusive),
	the third and fourth character (inclusive), and so on.

	D.  A charsetName element (with mandatory name attribute):
	specifies the characters which occur in the named set
	(names to be thought up later).

	E.  A choice element: specifies the union of its children.

	F.  A concur element: specifies the intersection of its children.

	G.  A difference element: specifies the non-symmetric difference
	of its children.

	H.  A kernel element: specifies the union of its children and
	some characters unknown.

	I.  A hull element: specifies the difference between its children
	and some characters unknown.

	J.  An alt element: specifies the characters known by its children.

Regex patterns may be used wherever data patterns may be used.
Kernels, hulls, and alt are explained at http://www.w3.org/TR/charcol/ .

-- 
John Cowan                              <jcowan@reutershealth.com>
http://www.reutershealth.com            http://www.ccil.org/~cowan
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