How does a selector look like?

Look at the following sample:

repository "default"
  path "/" label "release020"

This selector is telling the following to the system: work with a repository named default. Load all the elements from the root path, recursively, from a label called release020.

Complicated? Nothing compared to the daily problems a developer has to face and in exchange you get the following power:

repository "default"
  path "/doc"
    branch "/main/doc"
    checkout "/main/doc"
  path "/lib-GUI"
    branch "/main/stable" label "lib-stable-010"
  path "/"
    branch "/main/task0901" label "BL050"
    checkout "/main/task0901"

Which means: documentation will go directly to the doc branch; load libraries used for compilation from an stable location, in a read-only way; place your changes for the current task, task0901, in an associated branch, starting from the stable release BL050.

Powerful? Yes, and this is just the start.