I learned two things with this one little tidbit. First, adding Ctrl to the usual keyboard shortcuts for capturing screenshots will copy the screenshot to the clipboard rather than saving it to the Desktop. And second, hitting Spacebar after the initial keyboard shortcut activates windowed mode. You can then click on a specific window to get an exact screenshot of just that window with a transparent background and light drop shadow.
You can take a screenshot of a full window with a transparent background on MacOS using Cmd+Ctrl+Shift+4 then Spacebar.
July 1, 2019