(Note that this is not called a permalink but a fragment identifier
https://www.w3.org/Addressing/URL/4_2_Fragments.html or, more memorably, the hash part of the URL
https://developer.mozilla.org/en-US/docs/Web/API/URL/hash. Permalinks can be entirely different URLs, like a DOI link that is on a different domain and protocol altogether, but that will keep referring to this content
https://en.wikipedia.org/wiki/Permalink)