att.patternReplacement provides attributes for regular-expression matching and replacement. [16.2.3 Using Abbreviated Pointers Milestone Method 2.3.6 The Reference System Declaration Search-and-Replace Method]
Moduleheader — The TEI Header
MemberscRefPattern prefixDef
matchPatternspecifies a regular expression against which the values of other attributes can be matched.
Status Required

<rng:ref name="data.pattern"/>

The syntax used should follow that defined by W3C XPath syntax. Note that parenthesized groups are used not only for establishing order of precedence and atoms for quantification, but also for creating subpatterns to be referenced by the replacementPattern attribute.

replacementPatternspecifies a ‘replacement pattern’, that is, the skeleton of a relative or absolute URI containing references to groups in the matchPattern which, once subpattern substitution has been performed, complete the URI.
Status Required

<rng:ref name="data.replacement"/>

The strings $1, $2 etc. are references to the corresponding group in the regular expression specified by matchPattern (counting open parenthesis, left to right). Processors are expected to replace them with whatever matched the corresponding group in the regular expression.

If a digit preceded by a dollar sign is needed in the actual replacement pattern (as opposed to being used as a back reference), the dollar sign must be written as %24.