If you are looking for a class or symbol, you can type in any value. After you typed in the text you are searching for, you press Return. Now the tree gets filtered as well as the right pane with the symbols, lines, or customer objects.

Even if the symbol's texts aren't shown, they are filtered too.

Remark: Since the symbols or lines can be shown with their Class Display Name OR their Symbol Name the result of your filtering may be different.

You can see this if you use a visual style with the symbol's name.

If you click on the cross sign behind your search value...

...the whole tree will be collapsed with the exception of the tree node you may have previously selected.

You can also use a dropdown list with the text expressions you previously used for filtering.

Folder Links will be filtered the same way as classes, but only down to three levels. The image below shows, that valve was found under the folder below Assemblies.