https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode
https://emporem.com/sandbox/iframe/v29/host.html
https://robertnyman.com/html5/postMessage/postMessage.html
https://dev-bay.com/iframe-and-parent-window-postmessage-communication/
https://stackoverflow.com/questions/61548354/how-to-postmessage-into-iframe
https://www.snippetspub.com/Code/Web-KBSlider
https://www.codespeedy.com/dynamic-variable-names-in-javascript/
https://developer.mozilla.org/en-US/docs/Web/API/Window/frameElement
https://htmldom.dev/communication-between-an-iframe-and-its-parent-window/