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PieceĀ 

An atom, either a normal character, a character class, or a parenthesized regular expression, possibly followed by a quantifier.

Syntax

piece :: = atom quantifier?

Remarks

The following table shows valid pieces R and their set of strings L(R).

Valid pieces R for atoms S and non-negative integers n and m such that n<=m Set of strings L(R)

S

All strings in L(S).

S?

The empty string, and all strings in L(S).

S*

All strings in L(S?) and all strings ST with S in L(S*) and T in L(S).

All concatenations of zero or more strings from L(S).

S+

All strings ST with S in L(S) and T in L(S*).

All concatenations of one or more strings from L(S).

S{n, m}

All strings ST with S in L(S) and T in L(S{n-1, m-1}).

All sequences of at least n, and at most m, strings from L(S).

S{n}

All strings in L(S{n,n}).

All sequences of exactly n strings from L(S).

S{n,}

All strings in L(S{n}S*).

All sequences of exactly n strings from L(S).

S{0, m}

All strings ST with S in L(S?) and T in L(S{0, m-1}).

All sequences of at most m, strings from L(S).

S{0,0}

The set containing only the empty string.

See Also

Reference

XML Schema Regular Expressions
XML Schema Regular Expressions Reference Chart
Atom
Quantifier

Concepts

Data Type Facets