How do I create a m modifier in PHP PCRE? And what is a multi line?

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PHP

regular-expression

I am very confused about the m modifier and to make it more confusing i'm confused by the key word multi line. That word is used to describe the m modifier at most sources

online. So what does multi line mean in the use of a m modifier? Is a multi line multiple variables that contains strings or by the word multi line is it referring to

multiple new lines with the \n command in one variable string? And is multi line based on one string? If any one can adjust this code example below to give me the correct code structure for the m

modifier and a better understanding by the word multi line is referring to, I will really appreciate that. So I can understand the m modifier and the word multi line use in PHP regular expressions.

<?php
$string = 'JavaScript is cool and I love JavaScript.';
if(preg_match_all('/JavaScript/m',$string))
{
echo 'bla bla 1.';
}
else
{
echo 'bla bla 2';
}
?>

What I have tried:

Explained online but rare code examples of this is provider online.