How query for packages which have license A AND/OR license B

Unfortunately the search help page on pub.dev does not go into detail on boolean search expressions:
https://pub.dev/help/search

The goal here is to search for packages filtered by a list of licenses which should be either allowed or forbidden.

e.g. `license:mit,gpl-3.0` should list all packages with either MIT or GPL-3.0 license.

I was looking into implementing the filter functionality discussed here:
https://github.com/dart-lang/pub-dev/issues/4373

In this related issue: https://github.com/dart-lang/pub-dev/issues/5490 the option of adding search flags is discussed, but it seems like the license tag can only search for ONE license and not for multiple licenses (any of a given list).

`license:`

I tried the following:

`license:mit license:gpl-3.0` https://pub.dev/packages?q=license%3Amit+license%3Agpl-3.0
-> 2 Results with MIT && GPL-3.0

`license:mit,gpl-3.0` https://pub.dev/packages?q=license%3Amit%2Cgpl-3.0
-> 7 Results all MIT, I would expect all packages with either MIT or GPL-3.0

**Negating works:**

`license:mit -license:gpl-3.0` https://pub.dev/packages?q=license%3Amit+-license%3Agpl-3.0
-> 14874 (which is the list of all mit licensed packages minus those with two licenses)

`license:mit` https://pub.dev/packages?q=license%3Amit
-> 14876