Features of Cyrillic in PHP Regular Expressions

Cyrillic characters are not included in the \w group. To get them, you need to use a group in square brackets, like this: [а-я]. But even with this group there is a problem - the letter 'ё' will not be included here. To include it, you need to do this: [а-яё].

In addition, for the correct operation of Cyrillic in regex, it is necessary to set the u modifier:

<?php
	$str = 'яяя ййй ёёё';
	$res = preg_replace('#[а-яё]#u', '!', $str);
?>

Given a string:

<?php
	$str = 'wйw wяw wёw wqw';
?>

Write a regular expression that will find strings by the pattern: the edges are the letters 'w', and between them is a Cyrillic letter.

Given a string:

<?php
	$str = 'ааа ббб ёёё ззз ййй ААА БББ ЁЁЁ ЗЗЗ ЙЙЙ';
?>

Write a regular expression that will find all words by the pattern: any Cyrillic letter any number of times.