What are these escape sequences in the F# compiler source?

General
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1

What are the following escape sequences in the F# compiler source? These are from file lex.fsl.

Are these escapes sequences valid F# code or are they for the lexer generator?

let letter = '\Lu' | '\Ll' | '\Lt' | '\Lm' | '\Lo' | '\Nl'

let surrogateChar = '\Cs'

let digit = '\Nd'

let connecting_char = '\Pc'

let combining_char = '\Mn' | '\Mc'

let formatting_char = '\Cf'
2

Ah, I see. These seem to be Unicode Character Categories

3

On first sight these defined “letter” categories and sequences come across as different character related cases for the same character eg. Lu “uppercase” Ll “lowercase”.