What does the Ereg() function do?

Question

PHP

I got a staaary site on Bitrix. The component that displays (forms) the news has a line

if(strlen($arParams["FILTER_NAME"])<=0 || !ereg("^[A-Za-z_][A-Za-z01-9_]*$", $arParams["FILTER_NAME"]))
{
  $arrFilter = array();
}

Naturally, the modern version of php does not even know the ereg function (in 5.3 it became depricated, in 7 it is not at all). I replaced it one by one with

if(strlen($arParams["FILTER_NAME"])<=0 || !preg_match("^[A-Za-z_][A-Za-z01-9_]*$", $arParams["FILTER_NAME"]))
{
  $arrFilter = array();
}

The component works, but displays completely different news. What does this function actually do and how to replace it?

Answer 1

www.php.net/ereg