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<!-- Thank you very much for your pull request! If your PR is the addition of a new operator, please make sure all these boxes are ticked with an x: - [ ] Add the operator to Rx - [ ] It must have a `-spec.ts` tests file covering the canonical corner cases, with marble diagram tests - [ ] The spec file should have a type definition test at the end of the spec to verify type definition for various use cases - [ ] The operator must be documented in JSDoc style in the implementation file, including also the PNG marble diagram image - [ ] The operator should be listed in `apps/rxjs.dev/content/guide/operators.md` in a category of operators - [ ] The operator should also be documented. See [Documentation Guidelines](../CONTRIBUTING.md). - [ ] You may need to update `MIGRATION.md` if the operator differs from the corresponding one in RxJS v4 --> **Description:** <!-- If this PR introduces a breaking change, it must contain a notice for it to be included in the CHANGELOG. --> **BREAKING CHANGE:** <!-- add description or remove entirely if not breaking --> **Related issue (if exists):**