#### 3.1.4 Modification Request Numbers

MRs are identifiers that can be specified when checking in a revision using ‘`delta`’ (or even using ‘`admin`’, when creating a file).

If the ‘`v`’ (“validate”) flag is set, the user running ‘`delta`’ is prompted for MR numbers as well as revision comments. If this flag is not set, no validation is performed and no MR numbers are prompted for. If the `-m` option is given on the command line for `delta`, the user is not prompted.

MR numbers are not required by CSSC to be actual numbers; they may contain any non-whitespace printable characters; other implementations may not be so flexible.

MR numbers are frequently used to tie code revisions to other things, for example engineering change management documents or bug-tracking databases. If your change management systems are computer-based, you can use the validation program to ensure that the offered MR number is valid and that the calling user is allowed to change the file.

The first argument passed to the validation program is the name of the g-file and the following arguments are the MR numbers offered. The validating program should return zero if all the MR numbers are acceptable.

One might think that it would be useful to associate the MR number with the action of checking out for a modification (`get -e`), but this is not possible with SCCS. If you want to do that kind of thing, you must use a more advanced system, for example GNU CVS.