A tag adds a behavior to an object without changing the object itself. It is added from the context menu, in Tags, and removed from the same item. With several objects selected, it applies to all of them.

Objects with tags show their icons in the hierarchy. Clicking an icon shows the tag's settings in the properties panel, in place of the object's, and clicking the object goes back to it.

Primary camera

Cameras only. The public link and community posts open from this camera, even when it is not active in the editor. Only one camera has the tag at a time: giving it to another camera takes it from the previous one.

Without a primary camera, the active camera is used, and without one, the editor's perspective view.

Ghost

The object turns transparent bit by bit as the camera gets close to it, until it is gone. Useful for reference pieces, like the walls of a building around what is being built, that would block the view up close.

Starts fading: Distance, in meters, at which the object starts to turn transparent.
Fully gone: Distance at which it is fully gone.

The distance is measured to the edge of the object. On a group, everything inside counts as one piece: the distance goes to the edge of the whole group, and it all fades together. An object inside with its own tag fades on its own.

The effect shows in the viewport and in the public link. The selected object does not fade, so it stays easy to edit.