The restricted character set contains the characters that you can use for identifiers. It contains the following characters:
a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z
A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z
0, 1, 2, 3, 4, 5, 6, 7, 8, 9
_ (underscore)
These are the only characters that can be used. Other characters, such as accented characters and characters from other language sets are not supported. Also, identifiers used in scripts cannot begin with a number.