The URLSearchParams interface allows developers to (shock!) manipulate the search params of a URL. It also provides a mechanism to POST data via `fetch()` with a urlencoded body vs. the multipart body that `FormData` produces.
Docs: https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams/append
Samples: https://googlechrome.github.io/samples/urlsearchparams/index.html