You can use labels for annotation or categorization of any Topic. After clicking the Edit Topic Labels button a new window will be opened. Here you can manage all labels assigned to selected topic.
When adding a new label, labels from other topics are suggested.
You can remove labels one by one or all at once. The label editing screen can be accessed by clicking on label's name under each Topic.
All labels can be hidden by clicking Hide Labels. They will appear after editing or triggering button once again.
By clicking Toggle Estimates sum of numerical labels will be calculated for each topic. The sum of numeric labels is calculated sequentially from the leaves to the root topic. This sum will be added to its parent's topic. Numeric labels of topics with sum are ignored.
For example this can be used for adding up estimates on WBS (work-breakdown structure). You can add more than one numerical label and the sum will be calculated as range.