Automaton. Regular expressions are built from the following abstract syntax:
| regexp | ::= | unionexp | ||
| | | ||||
| unionexp | ::= | interexp | unionexp | (union) | |
| | | interexp | |||
| interexp | ::= | concatexp & interexp | (intersection) | [OPTIONAL] |
| | | concatexp | |||
| concatexp | ::= | repeatexp concatexp | (concatenation) | |
| | | repeatexp | |||
| repeatexp | ::= | repeatexp ? | (zero or one occurrence) | |
| | | repeatexp * | (zero or more occurrences) | ||
| | | repeatexp + | (one or more occurrences) | ||
| | | repeatexp {n} | (n occurrences) | ||
| | | repeatexp {n,} | (n or more occurrences) | ||
| | | repeatexp {n,m} | (n to m occurrences, including both) | ||
| | | complexp | |||
| complexp | ::= | ~ complexp | (complement) | [OPTIONAL] |
| | | charclassexp | |||
| charclassexp | ::= | [ charclasses ] | (character class) | |
| | | [^ charclasses ] | (negated character class) | ||
| | | simpleexp | |||
| charclasses | ::= | charclass charclasses | ||
| | | charclass | |||
| charclass | ::= | charexp - charexp | (character range, including end-points) | |
| | | charexp | |||
| simpleexp | ::= | charexp | ||
| | | . | (any single character) | ||
| | | # | (the empty language) | [OPTIONAL] | |
| | | @ | (any string) | [OPTIONAL] | |
| | | " <Unicode string without double-quotes> " | (a string) | ||
| | | ( ) | (the empty string) | ||
| | | ( unionexp ) | (precedence override) | ||
| | | < <identifier> > | (named automaton) | [OPTIONAL] | |
| | | <n-m> | (numerical interval) | [OPTIONAL] | |
| charexp | ::= | <Unicode character> | (a single non-reserved character) | |
| | | \ <Unicode character> | (a single character) |
The productions marked [OPTIONAL] are only allowed if specified by the syntax flags passed to the RegExp constructor. The reserved characters used in the (enabled) syntax must be escaped with backslash (\) or double-quotes ("..."). (In contrast to other regexp syntaxes, this is required also in character classes.) Be aware that dash (-) has a special meaning in charclass expressions. An identifier is a string not containing right angle bracket (>) or dash (-). Numerical intervals are specified by non-negative decimal integers and include both end points, and if n and m have the same number of digits, then the conforming strings must have that length (i.e. prefixed by 0's).
@lucene.experimental
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