After selecting some nodes, members or plates, this tool lets you hide all of the non-selected items. It is a quick way to isolate a selection visually without having to create a filter.
You can operate the tool by pressing the O key while holding down Shift and Ctrl (ie. Ctrl+Shift+O). If you press it again then the non-selected items become visible again. Alternatively, you can operate the tool by right-clicking and selecting "Show Selected Items Only".
The items that are hidden will be shown either transparent or invisible depending on the visibility setting at the bottom of the filters form.
If you start with a selection as follows.
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And then press Ctrl+Shift+O, the non-selected items become hidden as shown below. You can then continue to use any of the graphical input or editing tools on the visible items as normal.
To visually restore the hidden items you should press Ctrl+Shift+O again. If you continue to press Ctrl+Shift+O then the above cycle repeats.
The complementary tool to this one is the "Hide selected Items" tool which hides the selected items and keeps the non-selected ones visible.