Return the splitter that holds ``appletObj``.

        This method recursively searches for ``appletObj`` in the
        nested splitter hierarchy of the window layout, starting at
        ``split``. If successful, the method returns a reference to
        the splitter, otherwise it returns **None**.

        |Args|

        * ``appletObj`` (**QtmacsApplet**): the applet to look for.
        * ``split`` (**QtmacsSplitter**): the splitter where to begin.

        |Returns|

        * **QtmacsSplitter**: the splitter that holds ``appletObj``
          or **None**.

        |Raises|

        * **QtmacsArgumentError** if at least one argument has an invalid type.

def _qteFindAppletInSplitter(self, appletObj: QtmacsApplet,
                                 split: QtmacsSplitter):
        """
        Return the splitter that holds ``appletObj``.

        This method recursively searches for ``appletObj`` in the
        nested splitter hierarchy of the window layout, starting at
        ``split``. If successful, the method returns a reference to
        the splitter, otherwise it returns **None**.

        |Args|

        * ``appletObj`` (**QtmacsApplet**): the applet to look for.
        * ``split`` (**QtmacsSplitter**): the splitter where to begin.

        |Returns|

        * **QtmacsSplitter**: the splitter that holds ``appletObj``
          or **None**.

        |Raises|

        * **QtmacsArgumentError** if at least one argument has an invalid type.
        """
        def splitterIter(split):
            """
            Iterator over all QtmacsSplitters.
            """
            for idx in range(split.count()):
                subSplitter = split.widget(idx)
                subID = subSplitter._qteAdmin.widgetSignature
                if subID == '__QtmacsLayoutSplitter__':
                    yield from splitterIter(subSplitter)
            yield split

        # Traverse all QtmacsSplitter until ``appletObj`` was found.
        for curSplit in splitterIter(split):
            if appletObj in curSplit.children():
                return curSplit

        # No splitter holds ``appletObj``.
        return None