See Fetch Standatd at 4.7. CORS-preflight fetch

Note This is effectively the user agent implementation of the check to see if the CORS protocol is understood. The so-called CORS-preflight request. If successful it populates the CORS-preflight cache to minimize the number of these fetches.

at steps 1 through 7; also 4.8. CORS-preflight cache.

See the Fetch Standard, section 4.7. CORS-preflight fetch.

Note: This is effectively the user agent implementation of the check to see if the CORS protocol is understood. The so-called CORS-preflight request. If successful it populates the CORS-preflight cache to minimize the number of these fetches.

at steps 1 through 7; also 4.8. CORS-preflight cache.