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Any frame can be set as the anchor frame by hovering over the frame and selecting the Set as anchor button.
When a frame is set as the anchor frame, the frame cannot be edited in the viewport or Frame editor.
Frames Other frames that are not set as the anchor frame can be edited in the viewport and the Frame editor.
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The Visible/Hidden button allows you to show or hide the frame in the task viewport.
Frame editor
When a frame is selected in the Custom frames panel, the Frame editor on the right shows values for it.