So, you could add additional data to the automatically generated schema.

For example, you could decide to read and validate the request with your own code, without using the automatic features of FastAPI with Pydantic, but you could still want to define the request in the OpenAPI schema.

You could do that with `openapi_extra`:

```Python hl_lines="20-37  39-40"

     * @return The deserialized metadata, never {@code null}.
     * @throws IOException If the metadata could not be deserialized.
     * @throws MetadataParseException If the input format could not be parsed.
     */
    Metadata read(File input, Map<String, ?> options) throws IOException, MetadataParseException;

    /**

 files for and see if we can't incorporate it all into the POM. Or if we do
 have properties file (something I would like to avoid) say they don't
 contribute in any meaningful way to information in the POM. For example a
 properties file could be used the specify $ so it can be interpolated in
 <developerConnection/> but you couldn't use a properties file to specify the
 version of your project say. Anyway, food for thought to begin with.

This client could be a browser with a frontend, a code from someone else, an IoT device, etc.

You could need to tell the client that:

* The client doesn't have enough privileges for that operation.
* The client doesn't have access to that resource.
* The item the client was trying to access doesn't exist.
* etc.

 *       suite()} method with {@code Suppress}. Would {@code FooTest} itself be suppressed, too?
 *   <li>In at least one case, a use of {@code sun.misc.FpUtils}, the test will not even
 *       <i>compile</i> against Android. Now, this might be an artifact of our build system, one
 *       that we could probably work around. Or we could manually strip the test from open-source

Now, let's see how you could use that to return a custom response.

Let's say that you want to return an <a href="https://en.wikipedia.org/wiki/XML" class="external-link" target="_blank">XML</a> response.

   * FeatureSpecificTestSuiteBuilder.suppressing()}.
   */
  /*
   * TODO(cpovirk): or we could make HOLES_FORBIDDEN a feature. Or we could declare that
   * implementations are permitted to throw IAE if a hole is requested, and we could update
   * test*Hole to permit IAE. (But might this ignore genuine bugs?) But see the TODO above
   * testLower, which could make this all unnecessary
   */
  public static Method[] getHoleMethods() {

# OpenAPI Callbacks

You could create an API with a *path operation* that could trigger a request to an *external API* created by someone else (probably the same developer that would be *using* your API).

<img src="/img/tutorial/extending-openapi/image03.png">

## Change the Theme

The same way you could set the syntax highlighting theme with the key `"syntaxHighlight.theme"` (notice that it has a dot in the middle):

```Python hl_lines="3"
{!../../../docs_src/configure_swagger_ui/tutorial002.py!}
```

That configuration would change the syntax highlighting color theme:

<img src="/img/tutorial/extending-openapi/image04.png">

package com.google.common.eventbus;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.base.MoreObjects;

/**
 * Wraps an event that was posted, but which had no subscribers and thus could not be delivered.
 *
 * <p>Registering a DeadEvent subscriber is useful for debugging or logging, as it can detect
 * misconfigurations in a system's event distribution.
 *
 * @author Cliff Biffle
 * @since 10.0
 */