wp-includes/rest-api.php:1043Outputs the REST API link tag into page header.
function rest_output_link_wp_head() { $api_root = get_rest_url(); if ( empty( $api_root ) ) { return; } printf( '<link rel="https://api.w.org/" href="%s" />', esc_url( $api_root ) ); $resource = rest_get_queried_resource_route(); if ( $resource ) { printf( '<link rel="alternate" title="%1$s" type="application/json" href="%2$s" />', _x( 'JSON', 'REST API resource link name' ), esc_url( rest_url( $resource ) ) ); }}Introduced in 4.4.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/rest-api.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.