Source

File: wp-includes/rest-api/class-wp-rest-response.php

public function add_links( $links ) {
		foreach ( $links as $rel => $set ) {
			// If it's a single link, wrap with an array for consistent handling.
			if ( isset( $set['href'] ) ) {
				$set = array( $set );
			}

			foreach ( $set as $attributes ) {
				$this->add_link( $rel, $attributes['href'], $attributes );
			}
		}
	}