Turns out write works by appending the size into "px monospace", which allows you to use css properties. You can also use a slash, which allows you to have arbitrary units, including vw and vh. The viewport (the entire one, not just the stage) can be measured by writing something with size "100vh/1px monospace", where the size after the slash is the line spacing. Since snap only allows one line, it does nothing.
where's the code for the write block in the source? i want to look into this more but i can't find anything with "px monospace" or what function is actually called by the write block
the "browser is in full screen" block shouldn't be relied on, i've had screens with heights of 768, 1050, and 1024, and there are also many other common things such as 900, 864, 1152, 1536
when also considering phones and other portable displays it becomes impossible to detect anything. someone might even just have the browser the same height as a smaller resolution by accident.
you're almost definitely doing something wrong, the projet here works fine and isn't your website, or a website at all. creating snap projects and creating websites don't have much in common.
i'd just suggest reading the mdn docs and your code more closely.
It starts in a random position, and then writes the text to the right of that. If you want to center the text, you need to know how wide it is, which I don't check. This block just adds a few features to the original.