chore: add some comments about mimes (#18705)

Author: sapphi-red

packages/vite/src/node/constants.ts

@@ -116,6 +116,8 @@ export const CLIENT_DIR = path.dirname(CLIENT_ENTRY)
 //   add a mime type to the `registerCustomMime` in
 //   `packages/vite/src/node/plugin/assets.ts` if mime type cannot be
 //   looked up by mrmime.
+//   You can check if the mime type can be looked up by mrmime by running
+//   `node --print "require('mrmime').lookup('foo.png')"`
 export const KNOWN_ASSET_TYPES = [
   // images
   'apng',

packages/vite/src/node/plugins/asset.ts

@@ -48,6 +48,8 @@ export const cssEntriesMap = new WeakMap<Environment, Set<string>>()
 // add own dictionary entry by directly assigning mrmime
 export function registerCustomMime(): void {
   // https://github.com/lukeed/mrmime/issues/3
+  // instead of `image/vnd.microsoft.icon` which is registered on IANA Media Types DB
+  // image/x-icon should be used instead for better compatibility (https://github.com/h5bp/html5-boilerplate/issues/219)
   mrmime.mimes['ico'] = 'image/x-icon'
   // https://developer.mozilla.org/en-US/docs/Web/Media/Formats/Containers#flac
   mrmime.mimes['flac'] = 'audio/flac'