Looking for documentation for deco.curvedtext

[Sn3akyP3t3]

I understand this utility is heavily dependent on TeX so maybe that is where I'll find the answer to this question. I'm trying to understand what this means:

deco.curvedtext(r"\PyX{} is fun!")

from this example:
https://pyx-project.org/examples/text/textalongpath.html

The y in that example shows itself as subscript, but as uppercase. If I remove {} from the example it seems like the outcome is the same.

Where should I be looking for documentation or an explanation for what I'm seeing?