This file opens a new window at about:blank#, writes content into it, and
continuously enforces that the URL keeps the trailing #.
Note: Google usually blocks being embedded in an iframe via CSP/X-Frame-Options. This demo still injects the iframe and reports if it gets blocked.
If the new tab is blank or the URL becomes about:blank (without #), it usually means the browser
blocked the popup or prevented document.write. Allow popups for file:// (or open this file from a local server).