iframe_contentWindow = """
try {
    // Adds a contentWindow proxy to the provided iframe element
    const addContentWindowProxy = iframe => {
        const contentWindowProxy = {
            get(target, key) {
                // Now to the interesting part:
                // We actually make this thing behave like a regular iframe window,
                // by intercepting calls to e.g. `.self` and redirect it to the correct thing. :)
                // That makes it possible for these assertions to be correct:
                // iframe.contentWindow.self === window.top // must be false
                if (key === 'self') {
                    return this
                }
                // iframe.contentWindow.frameElement === iframe // must be true
                if (key === 'frameElement') {
                    return iframe
                }
                return Reflect.get(target, key)
            }
        }

        if (!iframe.contentWindow) {
            const proxy = new Proxy(window, contentWindowProxy)
            Object.defineProperty(iframe, 'contentWindow', {
                get() {
                    return proxy
                },
                set(newValue) {
                    return newValue // contentWindow is immutable
                },
                enumerable: true,
                configurable: false
            })
        }
    }

    // Handles iframe element creation, augments `srcdoc` property so we can intercept further
    const handleIframeCreation = (target, thisArg, args) => {
        const iframe = target.apply(thisArg, args)

        // We need to keep the originals around
        const _iframe = iframe
        const _srcdoc = _iframe.srcdoc

        // Add hook for the srcdoc property
        // We need to be very surgical here to not break other iframes by accident
        Object.defineProperty(iframe, 'srcdoc', {
            configurable: true, // Important, so we can reset this later
            get: function () {
                return _iframe.srcdoc
            },
            set: function (newValue) {
                addContentWindowProxy(this)
                // Reset property, the hook is only needed once
                Object.defineProperty(iframe, 'srcdoc', {
                    configurable: false,
                    writable: false,
                    value: _srcdoc
                })
                _iframe.srcdoc = newValue
            }
        })
        return iframe
    }

    // Adds a hook to intercept iframe creation events
    const addIframeCreationSniffer = () => {
        /* global document */
        const createElementHandler = {
            // Make toString() native
            get(target, key) {
                return Reflect.get(target, key)
            },
            apply: function (target, thisArg, args) {
                const isIframe =
                    args && args.length && `${args[0]}`.toLowerCase() === 'iframe'
                if (!isIframe) {
                    // Everything as usual
                    return target.apply(thisArg, args)
                } else {
                    return handleIframeCreation(target, thisArg, args)
                }
            }
        }
        // All this just due to iframes with srcdoc bug
        utils.replaceWithProxy(
            document,
            'createElement',
            createElementHandler
          )
    }

    // Let's go
    addIframeCreationSniffer()
} catch (err) {
    // console.warn(err)
}
"""