In terms of ManicTime, tags are some text values separated by a comma. Let's say you have these tags:
Client 1, Project 1
Client 1, Project 2
Client 1, Project 2, Activity 1
We could write these same tags as a hierarchy like this:
Client 1 Project 1 Project 2 Activity 1
To open Tag picker, click on a hierarchy icon in Tag window.
Tag picker will present the tags in a hierarchy view. You can click on the tags to go deeper in the hierarchy, or on the bread crumbs control above to go higher. When you find the correct tag, click Ok and it will be inserted into Tag view.
In a single user scenario, Tag picker will show previous tags you've used. When ManicTime is connected to the ManicTime server, it will also show all the tags defined on the server. So when it is connected to the server, it is a great tool for tag discovery.
If ManicTime is connected to ManicTime server, then tags in breadcrumb control will turn green when they are allowed.