code review

docs/custom-flows/overview.mdx

@@ -8,6 +8,17 @@ A _custom flow_ refers to a user flow created entirely from scratch using the Cl
 > [!TIP]
 > The information in this guide will help you get a general understanding of custom flow concepts. To skip to code examples, choose the guide that best fits your needs from the navigation on the left.
 
+<Details title="Read more about Publishable Keys">
+  When configuring your Clerk app, you'll need to provide a [Publishable Key](/docs/deployments/clerk-environment-variables#clerk-publishable-and-secret-keys). This key follows a specific format: it consists of your FAPI instance URL encoded in base64, prefixed with an environment identifier (e.g. `pk_test_` for development environments, `pk_live_` for production environments), and suffixed with a `$` delimiter for future extensibility. The base64-encoded URL enables your application to locate and communicate with your dedicated FAPI instance. You can verify this structure by decoding the key yourself:
+
+  ```js
+  const publishableKey = 'pk_test_ZXhhbXBsZS5hY2NvdW50cy5kZXYk'
+  const keyWithoutPrefix = publishableKey.replace('pk_test_', '')
+
+  atob(keyWithoutPrefix) // => example.accounts.dev$
+  ```
+</Details>
+
 ## How authentication flows work in Clerk
 
 Before building custom authentication flows, read the following sections to get a general understanding of how authentication flows work in Clerk.