Filesender hosts its code on github. For each major release there is a development branch which takes all new code via pull requests. When a release is made the changes on that development branch are considered locally to make a single patch which is then fed into the master branch just prior to the release.
This arrangement of development and master branches was desired by the Filesender board.
For the 2.x series changes should be made on a branch of development and a pull request made for the development branch on the Filesender github project.
For the 3.x bootstrap releases the development branch is called development3. The respective master branch is called master3.
This naming convention will allow future major releases to be made and avoid confusion about which git branch will match which major release.
As of the end of 2021 the 3.x series is still in prerelease so changes should be made on the 2.x series where possible and will be ported to the 3.x series. The obvious case where this does not apply is where the Bootstrap UI is to be updated where the PR should be made against development3.