Copy files from Install CD's where a file can be present either in normal or compressed format.
Compressed files often use the cabinet archiving method and usually have an identifiable character as the last character of their extensions. (e.g. myFile.Tx_ ). Windows XP often uses this method to compress files on the install CD.
DestinationFolderOrFilename means that you can either specify a folder where this file will be placed with the original (expanded) filename or new filename that you prefer.
In this example CopyOrExpand will first try to find a file c:\MyPath\myTextFile.txt and if it is not found then it will look for c:\MyPath\myTextFile.tx_ and expand this file if successfully found.