A repeat is an expression that is repeated an arbitrary number of times. An expression followed by "*" can be repeated any number of times including zero. An expression followed by "+" can be repeated any number of times, but at least once, if the expression is compiled with the flag regbase::bk_plus_qm then "+" is an ordinary character and "\+" represents a repeat of once or more. An expression followed by "?" may be repeated zero or one times only, if the expression is compiled with the flag regbase::bk_plus_qm then "?" is an ordinary character and "\?" represents the repeat zero or once operator. When it is necessary to specify the minimum and maximum number of repeats explicitly, the bounds operator "{}" may be used, thus "a{2}" is the letter "a" repeated exactly twice, "a{2,4}" represents the letter "a" repeated between 2 and 4 times, and "a{2,}" represents the letter "a" repeated at least twice with no upper limit.
Note: There must be no white-space inside the {}, and there is no upper limit on the values of the lower and upper bounds.
When the expression is compiled with the flag regbase::bk_braces then "{" and "}" are ordinary characters and "\{" and "\}" are used to delimit bounds instead. All repeat expressions refer to the shortest possible previous sub-expression: a single character; a character set, or a sub-expression grouped with "()" for example.
Examples:
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