warn_iframe_access = (iframe, error) => {
		/** @param {string} message */
		const log_template = (message) => [`OS-GUI.js failed to access an iframe (${element_to_string(iframe)}) for focus integration.
${message}
Original error:
`, error];

		let cross_origin;
		if (iframe.srcdoc) {
			cross_origin = false;
		} else {
			try {
				const url = new URL(iframe.src);
				cross_origin = url.origin !== window.location.origin; // shouldn't need to use iframe.ownerDocument.location.origin because intermediate iframes must be same-origin
			} catch (parse_error) {
				console.error(...log_template(`This may be a bug in OS-GUI. Is this a cross-origin iframe? Failed to parse URL (${parse_error}).`));
				return;
			}
		}
		if (cross_origin) {
			if (options.iframes?.ignoreCrossOrigin && !warned_iframes.has(iframe)) {
				console.warn(...log_template(`Only same-origin iframes can work with focus integration (showing window as focused, refocusing last focused controls).
If you can re-host the content on the same origin, you can resolve this and enable focus integration.
You can also disable this warning by passing {iframes: {ignoreCrossOrigin: true}} to $Window.`));
				warned_iframes.add(iframe);
			}
		} else {
			console.error(...log_template(`This may be a bug in OS-GUI, since it doesn't appear to be a cross-origin iframe.`));
		}
	}
@param {HTMLIFrameElement} iframe 
@param {Error | unknown} error