a \ (backslash) before the character. Any alpha-numeric character preceded by a backslash typically gives it a special meaning. In the case where the sequence has not been defined to be special, an error occurs. This is different to Perl, which gives an error only if it is in warning mode (PCRE2 does not have a warning mode). In basic POSIX regular expressions, sometimes backslashes escaped non-alpha-numerics (e.g. \.), and sometimes they introduced a special feature (e.g. \(\)). Extended character classes Single-letter character classes are supported in addition to the longer POSIX names. For example, \d matches any digit exactly as [[:digit:]] would in POSIX regular expressions. Minimal matching (a.k.a. "ungreedy") A ? may be placed after any repetition quantifier to indicate that the shortest match should be used. The default is to attempt the longest match first and backtrack through shorter matches: e.g. a.*?b would match first "ab" in "ababab", where a.*b would match the entire string. If the U flag is set, then quantifiers are ungreedy (lazy) by default, while ? makes them greedy. Unicode character properties Unicode defines several properties for each character. Patterns in PCRE2 can match these properties: e.g. \p{Ps}.*?\p{Pe} would match a string beginning with any "opening punctuation" and ending with any "close punctuation" such as [abc]. Matching of certain "normal" metacharacters can be driven by Unicode properties when the compile option PCRE2_UCP is set. The option can be set for a pattern by including (*UCP) at the start of pattern. The option alters behavior of the following metacharacters: \B, \b, \D, \d, \S, \s, \W, \w, and some of the POSIX character classes. For example, the set of characters matched by \w (word characters) is expanded to include letters and accented letters as defined by Unicode properties. Such matching is slower than the normal (ASCII-only) non-UCP alternative. Note that the UCP option requires the library to have been built to include Unicode support (this is the default for PCRE2). Very early versions of PCRE1 supported only ASCII code. Later, UTF-8 support was added. Support for UTF-16 was added in version 8.30, and support for UTF-32 in version 8.32. PCRE2 has always supported all three UTF encodings. Multiline matching ^ and $ can match at the beginning and end of a string only, or at the start and end of each "line" within the string, depending on what options are set. Newline/linebreak options When