Alphanumeric String Comparison In PHP [duplicate]

I am unable to understand how does PHP compare an alphanumeric string.

php > var_dump("222" < "30");
bool(false)

php > var_dump("222a" < "30");
bool(true)

The first comparison makes sense, but what’s happening in the second one ? how is it comparing last two digits from 222a with 30 ?

Thank You.