Such strings contain a character description delimited by single quotes '. The description is either just a character different from ' and \, or is \ followed by either a, b, t, n, v, f, r, \, ', or one, two or three octal digits representing a natural number smaller than $256$ (in decimal, for example '\11' represents $9$), or an x followed by one or two hexadecimal digits (uppercase or lowercase, for example '\xA1' represents $161$).