This option is available on the right click explorer context menu for MSI or MSM files. It is not available on WIN98-ME.
This option validates MSI (installer) or MSM (merge module) files.
It was written so that it can also be automated from a command line but this is as yet undocumented (or really tested).
Note that this command can take a while to run and the results will be displayed in notepad.
Keep in mind when validating databases (particularly when from other sources) that the "_Validation" table in the database is used a lot as a source of "rules".
If you get a validation message you believe is wrong you may wish to check this table to see if the relevant entries are correct.