For example, here is the current rawhide Xfce environment comps definition:

  <environment>
    <id>xfce-desktop-environment</id>
    <_name>Xfce Desktop</_name>
    <_description>A lightweight desktop environment that works well on low end machines.</_description>
    <display_order>15</display_order>
    <grouplist>
      <groupid>base-x</groupid>
      <groupid>standard</groupid>
      <groupid>core</groupid>
      <groupid>admin-tools</groupid>
      <groupid>dial-up</groupid>
      <groupid>fedora-release-nonproduct</groupid>
      <groupid>fonts</groupid>
      <groupid>input-methods</groupid>
      <groupid>multimedia</groupid>
      <groupid>networkmanager-submodules</groupid>
      <groupid>hardware-support</groupid>
      <groupid>printing</groupid>
      <groupid>guest-desktop-agents</groupid>
      <groupid>xfce-desktop</groupid>
    </grouplist>
    <optionlist>
      <groupid default="true">xfce-apps</groupid>
      <groupid default="true">xfce-media</groupid>
      <groupid>xfce-extra-plugins</groupid>
      <groupid>xfce-office</groupid>
      <groupid>3d-printing</groupid>
      <groupid>cloud-management</groupid>
    </optionlist>
  </environment>

I need a way, given an object for xfce-dekstop-environment, to list "xfce-apps" and "xfce-media". In yum this was exposed as yum.comps.Environment.defaultoptions.