Identifiers are the names of functions, variables and data structures.
Their format must, of course, follow the specifications of the rest of the text.
Identifiers contains letters, digits and underscores. An identifier must start with a letter.
An identifier must be unique ignoring case. Identifiers are case-insensitive. Two variables differing only in case are the same variable.
If an identifier is a reserved word in a language, it is appended with
x when writing to the language. If an identifier is a reserved word and
x is appended, etc. When reading from a language, the reverse is done.