docs: def initialize_environment(app):
      """
      Perform initializations needed before the build process starts.
      """
      env = app.builder.env
  
      # Assure ``traceability_all_items`` will always be there.
      if not hasattr(env, 'traceability_all_items'):
          env.traceability_all_items = {}
  
      update_available_item_relationships(app)