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regular_expressions.rst_
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re2c uses the following syntax for regular expressions: * ``"foo"`` case-sensitive string literal * ``'foo'`` case-insensitive string literal * ``[a-xyz]``, ``[^a-xyz]`` character class (possibly negated) * ``.`` any character except newline * ``R \ S`` difference of character classes ``R`` and ``S`` * ``R*`` zero or more occurrences of ``R`` * ``R+`` one or more occurrences of ``R`` * ``R?`` optional ``R`` * ``R{n}`` repetition of ``R`` exactly ``n`` times * ``R{n,}`` repetition of ``R`` at least ``n`` times * ``R{n,m}`` repetition of ``R`` from ``n`` to ``m`` times * ``(R)`` just ``R``; parentheses are used to override precedence or for POSIX-style submatch * ``R S`` concatenation: ``R`` followed by ``S`` * ``R | S`` alternative: ``R or S`` * ``R / S`` lookahead: ``R`` followed by ``S``, but ``S`` is not consumed * ``name`` the regular expression defined as ``name`` (or literal string ``"name"`` in Flex compatibility mode) * ``{name}`` the regular expression defined as ``name`` in Flex compatibility mode * ``@stag`` an *s-tag*: saves the last input position at which ``@stag`` matches in a variable named ``stag`` * ``#mtag`` an *m-tag*: saves all input positions at which ``#mtag`` matches in a variable named ``mtag`` Character classes and string literals may contain the following escape sequences: ``\a``, ``\b``, ``\f``, ``\n``, ``\r``, ``\t``, ``\v``, ``\\``, octal escapes ``\ooo`` and hexadecimal escapes ``\xhh``, ``\uhhhh`` and ``\Uhhhhhhhh``.