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The Layouts window can be opened from the toolbar menu Config > Layouts
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Use the + button below the Layout list panel to create a new layout, then right-click the new Layout within the Layout list and choose Rename to change its name.
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Within the Geometry settings of a Layer, set Position Mode to Lock to Region. A Region within a Layout can then be selected. Once a Region has been set, the Layer will be locked within the boundary of the Region.
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Show Layout
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The Show Layout toggle can be used to keep the selected layout visible once the Layouts window has been closed.