When creating new tags in Mercury, the option is there to define a tag as a 'Top Tag' or 'Other Tags'.
When adding the tag to a record or searching for contacts using the internal search, it will look the same as any other tag and will not be labelled any differently. It is simply there to be used if there is a group of tags, such as Location or Salary or year of qualification. The top tag would be used as the priority tag for your organisation. Other tags can be used for any given purpose.
These tag options were in Mercury before there was the functionality to make a tag mandatory. You may find that using mandatory tags may be more suitable, however the option to group tags differently may at times come in useful.
Tags can be added to contacts, clients and vacancy records.
Views and advanced find searches can be run to find records with a particular top tag.
NOTE: Only System Administrators who have had specific training can create new tags.