Processing method for special characters in Eregi_replace () _ Regular expressions

I'm not familiar with the regular expressions of PHP.
When you use the Eregi_replace () function, you find that a string with () cannot be replaced, read the manual or muddle through
Like what
Add DIN 1693 (pt.2)-1997 Bold
Use
$str = ' din 1693 (pt.2)-1997 '
Eregi_replace ($str, "<strong>". $str. " </strong> ", $STR);
Finally, because the string contains parentheses, it cannot be processed
Now I know it's wrong, but I don't know what the right way to write it.
That warrior can teach me how to deal with this problem? And also
If you use lowercase letters to query
Use this function to replace the original uppercase letters to lowercase, do not know how to keep the original writing (uppercase or lowercase)
I see Google as such.

?
$str = ' din 1693 (pt.2)-1997 ';
echo Preg_replace ("/(". Preg_quote ($STR). ") /"," <strong>\\1</strong> ", $str);
?>
Escape
Quotemeta
Preg_quote

If the Ereg function group uses Quotemeta
If the Preg function group uses preg_quote
echo Preg_replace ("/(". Preg_quote ($STR). ") /"," <strong>\\1</strong> ", $str);
\\1 is a reference to the found part, which preserves the original case.