protected void buildCompletionWindow() {
		if (focus == null) {
			// shouldn't happen; likely some off focus issue
			return;
		}

		completionWindow = new JWindow(WindowUtilities.windowForComponent(focus));
		completionWindow.add(content);
		content.setVisible(true);
		list.setVisible(true);
		Dimension size = getDefaultCompletionWindowDimension();
		if (-1 == size.height) {
			size.height = DEFAULT_HEIGHT;
		}
		if (-1 == size.width) {
			size.width = DEFAULT_WIDTH;
		}
		completionWindow.setSize(size);
	}
Build the completion window, parented to the attached field that last had focus.
Ghidra/Framework/Docking/src/main/java/docking/widgets/autocomplete/TextFieldAutocompleter.java