Output the content of the `PlaceholdeNode` in the template.

def render(self, context):
        """Output the content of the `PlaceholdeNode` in the template."""

        content = mark_safe(self.get_content_from_context(context))
        if not content:
            return ''
        if self.parsed:
            try:
                t = template.Template(content, name=self.name)
                content = mark_safe(t.render(context))
            except TemplateSyntaxError as error:
                if global_settings.DEBUG:
                    content = PLACEHOLDER_ERROR % {
                        'name': self.name,
                        'error': error,
                    }
                else:
                    content = ''
        if self.as_varname is None:
            return content
        context[self.as_varname] = content
        return ''