old_contents: from .factoranalysis import fa_feature_selection
  from .pca import pca_feature_selection
  from .rf import rfclassifier_feature_selection, rfregressor_feature_selection
  
  
  __all__ = [
      "fa_feature_selection",
      "pca_feature_selection",
      "rfclassifier_feature_selection",
      "rfregressor_feature_selection",
  ]
  
new_contents: from .factoranalysis import fa_feature_selection
  from .pca import PCAFeatures, pca_feature_selection 
  from .rf import RFFeatures, rfclassifier_feature_selection, rfregressor_feature_selection
  
  
  __all__ = [
      "PCAFeatures",
      "RFFeatures",
  
      "fa_feature_selection",
  ]
  
subject: add class; remove functional primitives