Means of regular expression ?

Answer 1

https://www.tutorialspoint.com/php/php_regular_expression.htm?_e_pi_=7%2CPAGE_ID10%2C7076646800

Answer 2

Did you ever tried to search for a string in another string? Well, instead of strings you can search for patterns. Those patterns are the regular expressions.
For example, instead of looping through a string and check if every character is a 0, you can check if a pattern is a number of zeros that start and end the string.
If you want I can provide a code :)