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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 fill_content(self, page, placeholder_slot):
 """ Add a placeholder to the page. Here we add a "TextPlugin" in all languages. """

        if len(placeholder_slot) == 1:
            raise RuntimeError(placeholder_slot)
        placeholder, created = self.get_or_create_placeholder(
            page, placeholder_slot)
        self.add_plugins(page, placeholder)