Identifiers (names for user variables, functions etc.) must begin with a letter, and this letter may be followed by any combination of letters or digits, provided that the name is not a reserved word (see the chapter on reserved words a complete list). In this definition the underscore _ is treated as a letter; but note that a single underscore is a reserved word. Identifier names are case-sensitive; that is, they are distinguished from one another by lower and upper case.
Intrinsic Magma functions usually have names beginning with capital letters (current exceptions include pCore, pQuotient and the like, where the p indicates a prime). Note that these identifiers are not reserved words; that is, one may use names of intrinsic functions for variables.