Source

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

public function add_link( $rel, $href, $attributes = array() ) {
		if ( empty( $this->links[ $rel ] ) ) {
			$this->links[ $rel ] = array();
		}

		if ( isset( $attributes['href'] ) ) {
			// Remove the href attribute, as it's used for the main URL.
			unset( $attributes['href'] );
		}

		$this->links[ $rel ][] = array(
			'href'       => $href,
			'attributes' => $attributes,
		);
	}