XQuery

Reluctant Quantifiers

XQuery supports reluctant quantifiers, which allow part of a regular expression to match the shortest possible string. Reluctant quantifiers are indicated by adding a question mark (?) to the end of any of the kinds of quantifiers identified in Table 18-1.

For example, given the string reluctant and the regular expression r.*t, the regular expression could match reluct or reluctant. Since a standard quantifier (*) is used, the match is on the longest possible string, reluctant. If the regular expression were r.*?t instead, which uses a reluctant quantifier, it would match reluct, the shorter of the two strings.

Reluctant quantifiers come into play when replacing matching values in a string. Table 18-12 shows some examples of calls to the replace function that use reluctant and nonreluctant quantifiers.

Table 18-12. Reluctant versus nonreluctant quantifiers

Example	Return value
replace("reluctant", "r.*t", "X")	X
replace("reluctant", "r.*?t", "X")	Xant
replace("aaah", "a{2,3}", "X")	Xh
replace("aaah", "a{2,3}?", "X")	Xah
replace("aaaah", "a{2,3}", "X")	Xah
replace("aaaah", "a{2,3}?", "X")	XXh

Reluctant quantifiers have no effect on simply determining whether a string matches a regular expression, which explains why they are not supported in XML Schema. It may seem that the regular expression r.*?tly would not match the string reluctantly because r.*?t would match the shorter string reluct, leaving an extra antly which does ...