What do lazy and greedy regular expressions mean?

Greedy expression tries to get as much as possible.
If you write a regular expression like this

<.+>

for the string:

<p>My expression</p>

you will get all the string

<p>My expression</p>

Oh, yes.. this thing is really greedy.

Let's take a look at the lazy one. If you write a regular expression like

<.+?>

We have just added "?". That means we want the smallest possible group. Now we have this result:

<p>

Here you are. The laziest thing you have ever seen :)

Method preg_match() for Cyrillic characters in PHP

Sometimes I encounter the problem with preg_match() method, because it doesn't treat Cyrillic characters the proper way. The problem also corresponds to other non-latin characters.
There is a solution for the search in the string that contains non-latin characters.

<?php 
  preg_match("/^[a-zA-Z\p{Cyrillic}]+$/u", "AбВгд");
?>

Do not forget about the Pattern Modifier - u

u (PCRE_UTF8)

This modifier turns on additional functionality of PCRE that is incompatible with Perl. Pattern strings are treated as UTF-8.

This modifier is available from PHP 4.1.0 or greater on Unix and from PHP 4.2.3 on win32. UTF-8 validity of the pattern is checked since PHP 4.3.5.