Config has a special document scope Install which allows for custom installation scripts:

App(version=1.0.0) {

  # Let's set some Env vars first
  Env {
    # so all child mechrons can reference this App
    app<App> = .;

    # let's ensure there is a UserBase for us (create one if not)
    users<UserBase> ?= create .:users<UserBase<OAuth<^10.0.0)>>>;

  Install {
    # set the bind property
    set .{ bind=${bundle}/bind/my-app.bind };

    # let's create a place to hold our Mechtrons
    create .:mechs<Base>;

    # and a place for holding user profiles
    create .:profiles<Base>;

    # Create a specific mechtron, notice we can reference
    # The bundle that THIS document came from using ${bundle} variable
    create .:mechs:my-mechtron<Mechtron>{ config=${bundle}:/config/my-mechtron.config +bind=${bundle}/my-mechtron.bind };

    # create the emailer
    create .:mechs:emailer<Mechtron>{ config=${bundle}:/config/emailer.config +bind=${bundle}/emailer.bind };

    # you can see we are now referencing env.users variable:
    grant perm +cSd-RwX on ${env.users}:**<User> to .:mechs:**;

    # the emailer needs to have Read permission on users' email addresses
    grant priv +prop:email<Read> on ${env.users}:*<User> to .:mechs:emailer;

    # users should have complete access to their profiles
    # notice we capture username from porfiles so it will match the username in user account
    grant +CSD-RWX on .:profiles:$(username) to ${env.users}:${username};

There's a lot going on there, but you can see that some important mechtrons are being created which are part of composing this application at install time.