Description:
------------
http://unicode-table.com/ru/#cyrillic

Can you make what 'а-я'  (0430 - 0439)  expression include literal 'ё' (0451)
becouse russian alphabet contains this char in middle of list

Kinda got problems when make surname check or etc.

Test script:
---------------
	$surname = 'ёмобиль';
	
	$res = preg_match('/^([а-я]+)$/iu', $surname);

	if(!$res) {
		echo 'Фамилия содержит не корректные символы';
		echo 'Surname contains non-valid characters';
	}

//  preg_match not see char 'ё' 


//  preg_match('/^([ё-я]+)$/iu', $surname);
//  make Warning  even caseless mode set

//  preg_match('/^([Ё-я]+)$/iu', $surname);  //  work as should