Compared with Python, there is no P in the syntax for named groups. The named backreference is \k or \k'name'.
(? group ) or (?'name' group ) captures the match of group into the backreference “name”. Microsoft’s developers invented their own syntax, rather than follow the one pioneered by Python and copied by PCRE (the only two regex engines that supported named capture at that time). The HTML tags example can be written as * ) \b * >. Though the syntax for the named backreference uses parentheses, it’s just a backreference that doesn’t do any capturing or grouping. The question mark, P, angle brackets, and equals signs are all part of the syntax. You can reference the contents of the group with the named backreference (?P=name). name must be an alphanumeric sequence starting with a letter. (?P group ) captures the match of group into the backreference “name”.
Python’s re module was the first to offer a solution: named capturing groups and named backreferences. They can be particularly difficult to maintain as adding or removing a capturing group in the middle of the regex upsets the numbers of all the groups that follow the added or removed group. Long regular expressions with lots of groups and backreferences may be hard to read. Nearly all modern regular expression engines support numbered capturing groups and numbered backreferences. Named Capturing Groups and Backreferences
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