A keynote parameter is available for all model elements (including detail components) and materials. You can tag each of these elements using a keynote tag family. The keynote value is derived from a separate text file that contains a list of keynotes.
If an element already contains a value for a keynote, it displays in a tag automatically. If not, you can select the keynote value directly. Revit provides 2 sample text files for keynoting. See Keynote Workflow.
Keynotes assigned in a project are linked to their source keynote table. When the keynote table is changed, keynotes in the project will reflect the changes when the project is closed and reopened.