How does PHP regular expression preg_match implement the matching function?

The example of this article describes the implementation of regular expression matching function by PHP preg_match. Share it with everyone for your reference, the details are as follows:

preg_match — Execute a regular expression match

preg_match ( $pattern , $subject , $matches )

Search for the regular expression given by subject and pattern A match.

Parameters:

pattern : Pattern to be searched, string type (regular expression).
subject : Input string.
matches : (optional) If the parameter matches is provided, it will be populated as search results. $matches[0] will contain the text matched by the full pattern, $matches[1] will contain the text matched by the first captured subgroup, and so on.

Return value:

preg_match() returns the number of matches for pattern. Its value will be 0 (no match) or 1 because preg_match() will stop searching after the first match. preg_match_all() differs from this in that it searches for the subject until it reaches the end. If an error occurs preg_match() returns FALSE.

Instance 1:

$label = 'content/112';
$a = preg_match('#content/(\d+)#i', $label, $mc);
var_dump($a);
var_dump($mc);

Output:

int(1)
array(2) {
 [0]=>
 string(11) "content/112"
 [1]=>
 string(3) "112"
}

Instance 2:

$label = 'content/112';
$a = preg_match('#(\w+)/(\d+)#i', $label, $mc);
var_dump($a);
var_dump($mc);

Output:

int(1)
array(3) {
 [0]=>
 string(11) "content/112"
 [1]=>
 string(7) "content"
 [2]=>
 string(3) "112"
}

Instance 3:

$label = 'content/112';
$a = preg_match('#content1111111/(\d+)#i', $label, $mc);
var_dump($a);
var_dump($mc);

Output:

int(0)
array(0) {
}

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