Instructor: Here we have a running Gatsby site, an mdx file and the result of that mdx file. Note that our Gatsby site is configured with Gatsby MDX because we haven't passed in any options like we have for other plugins.
It's using the default config. The default configuration for Gatsby MDX only applies to files with .mdx in the file name.
Note that moving the pageThree.mdx file to pageThree.md results in a page that doesn't exist because Gatsby MDX has not set up to process .md files.
To enable Gatsby MDX to process .md files, as well as .mdx files, we'll use the extensions option in Gatsby MDX's config. Note that any time you change the Gatsby config.js file, you must restart the Gatsby process.
Now when we refresh the page, we can see that pageThree.md is now considered an MDX file.