Identifiers

All variables, functions, and object properties are named with identifiers. ActionScript identifiers must be composed according to the following rules:

• Identifiers must include only letters (A-Z or a-z), numbers, underscores, and dollar signs. Be especially careful never to use spaces, periods, backslashes, or other punctuation in identifiers.
• Identifiers must start with a letter, underscore, or dollar sign (not a number).
• Identifiers may not be identical to reserved words.

Though not strictly required, it's also good practice to follow the preceding rules when composing movie clip instance names, frame labels, and layer names.