In the dialog box definition file (.DLG), most of the text strings in the dialog box start with an at sign (@). This is the mechanism by which a single dialog box can be used for multiple purposes inside a setup script. If the text is @Text1, for example, the script can set a symbol called Text1 to some arbitrary text before displaying the dialog box, and when the dialog box appears, the new text will occupy the position where @Text1 appears in the dialog box definition. This also applies to list box titles, button labels, and so on.
One good use for this feature is error handling — a single dialog box with caption @ErrorString, text @ErrorDesc, and buttons @Button1 and @Button2 could be used to display information about many different errors. For example, set ErrorString=Fatal Setup Error and ErrorDesc=Some Important File Is Corrupted. The buttons at the bottom of the dialog box could be changed by setting Button1=Ignore Error and Button2=Try Again. See the existing .INF scripts for examples.