3. The non-transitory machine-readable storage medium of claim 2 , wherein: the feature is associated with a feature type, identifying the feature in the plurality of training documents further comprises identifying a corresponding feature type for the feature, and a feature type decision tree is generated that comprises the feature type.
5. The non-transitory machine-readable storage medium of claim 3 , wherein the feature type is: a raster, a title, an image object, a text string, a word, a unique mark, a unique character, a numeric code, or a non-human readable marking.