To make changes with the mergeprop utility, you must list the affected groups and properties in adelta file. The delta file must specify at least one property group; it can also specify one or more properties and associated values. The content of the delta file must conform to the syntax rules for property files, as explained in Logical structure and syntax of property files .

The delta file is expressed as an argument to the -delta command or as a parameter to the setTargetFile() or mergeprop() method.