ActionScript for Flash MX: The Definitive Guide, Second Edition

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Chapter 15: Lexical Structure

• For safety, identifiers should include only letters (A–Z or a–z), numbers, under-

scores, and dollar signs. Be especially careful never to use spaces, periods,

backslashes, or other punctuation in identifiers. However, most Unicode char-

acters are, in fact, permitted in identifiers, according to the rules outlined in

section 3.16 of the Unicode standard. (See http://www.unicode.org/unicode/

standard/standard.html).

• A character in an identifier cannot be specified with a Unicode escape sequence

(\uxxxx). (This is a departure from ECMA-262, v3, which allows escape

sequences in identifiers.)

• See the next section on case-sensitivity for more caveats about identifiers.

Though not strictly required, it’s also good practice to follow these rules when com-

posing movie clip instance names, symbols, symbol export identifiers, frame labels,

and layer names. For information on using standardized suffixes in identifier names

(such as

_mc to indicate a movie clip) see Table 2-1 in Chapter 2.

Case Sensitivity

When a language is fully case sensitive, every token in the language—including all

identifiers and keywords—must be entered with the correct capitalization. For exam-

ple, in case-sensitive languages, the statement:

If (x = = 5) {

x = 10;

}

would cause an