When you compile ABL procedures for your WebClient application, the compiler generates an r-code signature value, a fixed-length value that is unique for the exact contents of a given source code file.

If the source code of the procedure changes recompiling the file generates a different r-code signature value. Later, when you deploy a new version of your application using the WebClient Application Assembler, the Assembler compares the existing and new r-code signature values. If the values are different, the Assembler assumes that the new file has changed and marks it as an update of the old file.