Source

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

public function response_to_data( $response, $embed ) {
		$data  = $response->get_data();
		$links = self::get_compact_response_links( $response );

		if ( ! empty( $links ) ) {
			// Convert links to part of the data.
			$data['_links'] = $links;
		}

		if ( $embed ) {
			$this->embed_cache = array();
			// Determine if this is a numeric array.
			if ( wp_is_numeric_array( $data ) ) {
				foreach ( $data as $key => $item ) {
					$data[ $key ] = $this->embed_links( $item, $embed );
				}
			} else {
				$data = $this->embed_links( $data, $embed );
			}
			$this->embed_cache = array();
		}

		return $data;
	}