Performs the actual loading of an external resource into the current model.

        Args:
            ctx: The processing context.

        Returns:
            Returns a dictionary that gets incorporated into the actual model.

def _apply(self, ctx: ExtensionContext) -> AugmentedDict:
        """
        Performs the actual loading of an external resource into the current model.

        Args:
            ctx: The processing context.

        Returns:
            Returns a dictionary that gets incorporated into the actual model.
        """
        def process(pattern: Pattern[str], _str: str) -> Any:
            _match = pattern.match(_str)
            if _match is None:
                return _str  # pragma: no cover
            # We got a match
            # Group 0: Whole match; Group 1: Our placeholder;
            # Group 2: file path to external resource
            placeholder, external_path = _match.group(1), _match.group(2)
            with open(self.locator(
                    external_path,
                    cast(str, ctx.document) if Validator.is_file(document=ctx.document) else None
            )) as fhandle:
                # Json does not support line breaks. We will have to mask them
                content = fhandle.read()
            return _str.replace(placeholder, content)

        node_key, node_value = ctx.node
        _pattern = re.compile(self.__pattern__)
        return {node_key: process(_pattern, node_value)}