Automatic automatic extraction
    "ConformedData" conformed images, colors, dates, etc.
    "DiscretizedVector" discretized numerical data
    "DimensionReducedVector"    reduced-dimension numeric vectors
    "FaceFeatures"  semantic vector from an image of a human face
    "ImageFeatures" semantic vector from an image
    "IndicatorVector"   nominal data "one-hot encoded" with indicator vectors
    "IntegerVector" nominal data encoded with integers
    "MissingImputed"    data with missing values imputed
    "NumericVector" numeric vector from any data
    "PixelVector"   vector of pixel values from an image
    "StandardizedVector"    numeric data processed with Standardize
    "SegmentedCharacters"   text segmented into characters
    "SegmentedWords"    text segmented into words
    "TFIDF" term frequency-inverse document frequency vector
    Identity    give data unchanged
    {Subscript[extractor, 1],Subscript[extractor, 2],[Ellipsis]}   use a sequence of extractors in turn