How to check if a string consists of only one type of character?

Hi, how do I check if a string only consists of one character type? e.g A string that contains only a's ('aaaaaaaaaaaaaaaa')

I have something. Put it in Workspace:

for i,v in pairs(workspace:GetChildren()) do
	if v.Name == "aaaaaaaaaaaaaaaa" then
		print("b")
	end
end

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