wp-includes/class-wp.php:93Adds a query variable to the list of public query variables.
$qvstring public function add_query_var( $qv ) { if ( ! in_array( $qv, $this->public_query_vars, true ) ) { $this->public_query_vars[] = $qv; } }Introduced in 2.1.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.