Python An Array whose contents depend on the presence or absence of the global (g) flag, or null if no matches are found. Substituted with the text matched between the 1st through 9th numbered capturing group. In Regex, capturing parenthesis allow us to match a value, and remember it. std::regex Backreferences can be used inside the group they reference. Use the constructor function when you know the regular expression pattern will be changing, or you don't know the pattern and obtain it from another source, such as user input. There are two ways to create a RegExp object: a literal notation and a constructor. The following grouping construct captures a matched subexpression:( subexpression )where subexpression is any valid regular expression pattern. They allow you to apply regex operators to the entire grouped regex. Named capture with (?…), backreference \k and replacement insertion ${foo} Unicode properties such as \p{L} Amazingly, XRegExp does not support lookbehind. Perl .NET The caret and dollar always match at embedded line breaks in std::regex, while in JavaScript and POSIX this is an option. Starting with ECMAScript 6, new RegExp(/ab+c/, 'i') no longer throws a TypeError ("can't supply flags when constructing one RegExp from another") when the first argument is a RegExp and the second flags argument is present. A very cool feature of regular expressions is the ability to capture parts of a string, and put them into an array. Java XRegExp To match characters from other languages such as Cyrillic or Hebrew, use \uhhhh, where hhhh is the character's Unicode value in hexadecimal. Capturing group \(regex\) Escaped parentheses group the regex between them. No mode modifiers to set matching options within the regular expression. The line splitting provided in this example works on all platforms. XRegExp You construct a regular expression in one of two ways:Using a regular expression literal, which consists of a pattern enclosed between slashes, as follows:Regular expression literals provide compilation of the regular expression when the script is loaded. in the pattern \d+ (?=€), the € sign doesn’t get captured as a part of the match. Substituted with the text matched between the 1st through 99th numbered capturing group. With JavaScript, you can group s part of regular expression. When using the constructor function, the normal string escape rules (preceding special characters with \ when included in a string) are necessary. Boost Backreferences can be used before the group they reference. A new RegExp from the arguments is created instead. Your regex should have two spaces separating the three numbers. Use numbered capturing groups instead. Use literal notation when the regular expression will remain constant. 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