Used on the Macintosh to convert a 4-character constant to a value that may be used by Dir, Kill, Shell, and AppActivate.
The required constant argument consists of 4 characters used to specify a resource type, file type, application signature, or Apple Event; for example, TEXT, OBIN, "XLS5" for Excel files ("XLS8" for Excel 97); Microsoft Word uses "W6BN" ("W8BN" for Word 97), and so on.
MacID is used with Dir and Kill to specify a Macintosh file type. Because the Macintosh does not support * and ? as wildcards, you can use a four-character constant instead to identify groups of files. For example, the following statement returns TEXT type files from the current folder:
MacID is used with Shell and AppActivate to specify an application by using the application's unique signature.