This command generates a BookVars file from the variable definitions that exist in the selected file(s). Once you have generated a BookVars file, you can use the Edit BookVars File command to modify the variable definitions, and then use the Import Variables command to import those variable definitions into all files in the book.
A BookVars file can contain multiple variable groups. If you define multiple groups in a single BookVars file you can switch between those groups to easily update variable definitions for different products or languages. You can add additional groups to the BookVars file with the Update BookVars File command.