Why isn't {} a part of the syntax highlight leanEncl group?

[nguyenvukhang]

Just curious, why isn't {} included in this list?

" delimiters
syn region leanEncl matchgroup=leanDelim start="#\[" end="\]" contains=TOP
syn region leanEncl matchgroup=leanDelim start="(" end=")" contains=TOP
syn region leanEncl matchgroup=leanDelim start="\[" end="\]" contains=TOP
syn region leanEncl matchgroup=leanDelim start="⦃"  end="⦄" contains=TOP
syn region leanEncl matchgroup=leanDelim start="⟨"  end="⟩" contains=TOP

syn region leanAnonymousLiteral matchgroup=leanDelim start="⟨"  end="⟩" contains=TOP

[Julian]

IIRC because doing so causes issues with structure literals ({ foo := bar, baz := quux }) but I'd have to remind myself honestly.

If you see any broken highlighting as is definitely share.

[nguyenvukhang]

I see, but I'm not sure if I can reproduce that on my setup.

Here's how it looks with the current syntax highlighting provided by the plugin:

and then after adding this line:

syn region leanEncl matchgroup=leanDelim start="{" end="}" contains=TOP

here's how it looks like:

I also did a quick check with vim.fn.synIDattr() to see what syntax highlight group was caught in the first picture. There was none. For the second one it was { "leanEncl", "leanDelim" } for both the optional arguments and the structure literals.