Inside a domain name you can
Lowercase english alfabet from "a" to "z".
Number from 0 to 9. Sign minus "-"
You CAN NOT use: aritmetics simbols, character like &,%,?,$,? ), "_" , ? ? ? ? ecc and capital letter.
Minimum lengh for .it domain is 3 character without extension.
Max lenght for .it domain is 26 character without extension.
MAx lenght for .net .com .org .info .biz is 63 character with extension included. 3 in minimum leght allowed.