Compatibility: Version 6.8.x and 2003.x
When manipulating files in 4D, you might come across a problem where you want to perform some action only on certain types of files. In this case, you will have to be able to accurately identify the extension of a file. Filenames can contain periods in them, so it is not safe to assume that the extension of a file is immediately after a period in the filename.
For example, the extension of "myfile.old.txt" is "txt" not ".old.txt." The following method correctly extracts the extension of a filename and either returns the extension or null string if there is no extension.
` find the position of the last period
While (($len>0) & ($char#"."))