# Why is the alternative to GridSearchCV in RandomForestClassifier documented to be OOB?

The sklearn documentation for gridsearch (link) puts "3.2.4.3. Out of Bag Estimates" in a subsection under "3.2.4. Alternatives to brute force parameter search." I understand each of grid search and OOB, but I don't understand how it's an "alternative." For example, if I need to determine the ideal max_features parameter to use with RandomForestClassifier, how would I use OOB instead of GridSearch? I can imagine for example using GridSearch with the scoring parameter being a callable returning the OOB, but it's not really an alternative as much as a "complementary" feature.