Question: Why can't I delete the result of Explore from my Document?

I created a new Document with a single command:


Then I right-clicked on the command and chose Explore from the context menu and then clicked on the Explore button in the dialog box. A rectangle with a slider appeared. So far so good.  However, I cannot delete the rectangle from my Document. I tried to select the rectangle and press Delete, Ctrl+Delete, and to right-click on it and choose Cut from the menu. Nothing works.

If I select both the rectangle and the command A=1 all the three actions described above also fail to delete anything.

Help will be appreciated.

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