When used with the autocat attribute, autocatPrune="true" indicates that taxonomy pruning should be used during categorization.

<query autocat="max" autocatPrune="prune"

This process eliminates any category assignments in which content is assigned to a child category where it should also be assigned to the parent. For example, a taxonomy has a category for Product X and subcategories containing topics, such as Installation, Service, Support, Help, etc. Without pruning, the taxonomy rules would be forced to require X in the rules throughout the sub-tree, such as “support for X” and “install X”. This might be possible, but often X won’t be in the same sentence as the other terms required for the sub-categories. With pruning, the taxonomy rules could simply define rules for X under the root product X category, then define generic rules for the sub-tree, like “support” and “install”. Content that matched these generic rules and was assigned to the categories would be pruned if it was not also assigned to the product X category. Taxonomy pruning works globally across all categories, effectively pruning content down the tree that has not been assigned above it.