Help me understand this PHP code

Question

I am a PHP beginner.

When going through a PHP script I found:

if(preg_match('/(?i)ID=(\d+)/',$input)) {
    // id found
}

I want to know what does (?i) mean ?

Answer 1

(?i) is a in line modifier which makes the match case insensitive.

It is equivalent to adding a i after the closing delimiter:

if(preg_match('/ID=(\d+)/i',$input))
                         ^

Answer 2

The below line is finding matching pattern in $input string like ID=any number.

preg_match('/ID=(\d+)/i',$input)

Example matching patterns are ID=2 id=34 Id=23