Here's a "Hello World" with a whole ton of loops as well :)

https://imgur.com/fhG2Fwq

That's a totally acceptable "helloooooooo world"!

The model was trained on a relatively small dataset which has few occurrences of the letter x, almost none of which are in cursive. As you've found, asking the model to write out an x in a cursive style can totally derail the generation process.

Any ELI5 for people who know close to nothing about NN, AI, machine learning etc?

Like, how does one letter it doesn't know how to write well make it skip/mess up the following ones too? I mean, "derail" seems a fitting description to what I'm seeing, but how?

The "handwriting" data for this model is basically the coordinates of a pen. The length of the string representation of the text is very different from the length of the coordinate representation of the text, therefore the model "learns" a window corresponding to when it is drawing the current letter, and when to start the next letter. For these letters, as the model doesn't learn how long this window should be, nor how to transition from it to the next letter, it gets stuck and outputs nonsense.

There must not have been many "z"s either -- "quartz" failed as much as "fox" in my tries. Still, nice work!

I got that to after playing around a bit and then trying that phrase. It gave me a really good laugh, as if AI just went "ah shit, why does everyone enter this stupid phrase eventually?"