Where is version information stored?

Both software version numbers and product version numbers are found in the version field of the component’s or metapackage’s composer.json file.

For example, you can declare software version as a version of the component:

"name": "acme/foo",
"version": 1.2.0

Or you can use it to declare a dependency on a particular version of a component:

"require": {
   "acme/foo": "1.2.*",
   "acme/bar": "2.2.0"