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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def addUnderlineAnnot(self, rect):
 """Underline content in a rectangle or quadrilateral."""

        CheckParent(self)

        val = _fitz.Page_addUnderlineAnnot(self, rect)

        if not val: return
        val.thisown = True
        val.parent = weakref.proxy(self)
        self._annot_refs[id(val)] = val

        return val