The assembler handles the same strings as assembler directives and mnemonics as reserved words. These reserved words have special functions and they cannot be used as label names or symbol names in assembly-language files. They are not case-sensitive; for example, "ABS" and "abs" are the same reserved word.

Reserved words are classified into the following types.

All assembler directives and all strings that begin with a period (.).

All mnemonics of the RX Family.

All register and flag names of the RX family.

All operators described in this section.

A system label is a name that begins with two periods and is generated by the assembler. All system labels are handled as reserved words.