What is the significance of the "m" modifier in a regular expression pattern in PHP, and when should it be used?

The "m" modifier in a regular expression pattern in PHP is used to indicate that the pattern should be applied in multiline mode. This means that the "^" and "$" anchors will match the start and end of each line within the subject string, rather than just the start and end of the entire string. The "m" modifier should be used when you want to match patterns across multiple lines within a string. 

$subject = "Hello\nWorld";
$pattern = '/^H.*$/m';
if (preg_match($pattern, $subject)) {
    echo "Pattern found in multiline mode.";
} else {
    echo "Pattern not found.";
}

Keywords

PHP regular expression m modifier pattern significance

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