KaTeX dies when attempting to render \begin\displaystyle

[Aresiel]

Before reporting a bug

• Check common issues.
• Check the bug is reproducible in the demo. If not, check KaTeX is up-to-date and installed correctly.
• Search for existing issues.

Describe the bug:
Attempting to render \begin\displaystyle causes KaTeX to crash with the error message "Expected node of type textord, but got node of type styling".

To Reproduce:
Steps to reproduce the behavior:

1. Go to https://katex.org/
2. Write \begin\displaystyle in the demo box
3. See error in box directly to the right of demo box

Expected behavior:
I expect it to either render correctly as LaTeX (whatever this now entails), or for KaTeX to display it as invalid LaTeX as usual.

Screenshots:

Environment (please complete the following information):

• KaTeX Version: 0.16.10
• Device: Desktop
• OS: Windows 11
• Browser: Firefox
• Version: 125.0b7

Additional context:
This issue originally occured on a separate site, but as it's reproducable on https://katex.org/, that ought not matter.

[edemaine]

I guess this input should generate a KaTeX parse error instead of a general error, but otherwise this behavior seems correct.

For comparison, LaTeX generates the cryptic error Missing \endcsname inserted. 🙂