Question about the variables

[Illuminings]

I want to know why sometimes, the variables that don’t have the ‘local’ in front of it aren’t marked as error or underlined but other times, it does. Here is what I meant:
Not marked as error

Marked as error

[Uhsleep91]

When you hover over the variable, what does it say?

[index_self]

In Lua (and Luau, but not supported with analysis), variables are always global unless you tag them with local.

local function f()
	a = 1
end

print(a) -- 1

In normal Lua, all globals are put inside the environment table (getfenv()), which is by default _G.

Roblox changed the behavior of _G so that it was just a blank shared table across scripts, and its use and global variables are now obsolete.