wp-includes/canonical.php:790Converts the first hex-encoded octet match to lowercase.
$matchesarraystring function lowercase_octets( $matches ) { return strtolower( $matches[0] ); }Introduced in 3.1.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/canonical.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.