description: One or more labels that indicate a specific set of
                      pods/VMs on which the configuration should be applied.
                    maxProperties: 256
                    type: object
                type: object
            type: object
            x-kubernetes-validations:
            - message: only one of targetRefs or workloadSelector can be set

## Documenting the callback

The actual callback code will depend heavily on your own API app.

And it will probably vary a lot from one app to the next.

It could be just one or two lines of code, like:

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
httpx.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

///

/// check

OpenAPI specifies that each *path operation* requires a response description.

So, if you don't provide one, **FastAPI** will automatically generate one of "Successful response".

///

<img src="/img/tutorial/path-operation-configuration/image03.png">

## Deprecate a *path operation*

package com.google.common.collect.testing.testers;

import static com.google.common.collect.testing.features.CollectionFeature.REJECTS_DUPLICATES_AT_CREATION;
import static com.google.common.collect.testing.features.CollectionSize.ONE;
import static com.google.common.collect.testing.features.CollectionSize.ZERO;

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.testing.features.CollectionFeature;

    @Override
    public BigInteger next(BigInteger value) {
      return value.add(BigInteger.ONE);
    }

    @Override
    public BigInteger previous(BigInteger value) {
      return value.subtract(BigInteger.ONE);
    }

    @Override
    BigInteger offset(BigInteger origin, long distance) {
      checkNonnegative(distance, "distance");

# Sub Applications - Mounts

If you need to have two independent FastAPI applications, with their own independent OpenAPI and their own docs UIs, you can have a main app and "mount" one (or more) sub-application(s).

## Mounting a **FastAPI** application

"Mounting" means adding a completely "independent" application in a specific path, that then takes care of handling everything under that path, with the _path operations_ declared in that sub-application.

				return true
			}
		}
	}

	// x-amz-copy-source-if-match : Return the object only if its entity tag (ETag) is the
	// same as the one specified; otherwise return a 412 (precondition failed).
	ifMatchETagHeader := r.Header.Get(xhttp.AmzCopySourceIfMatch)
	if ifMatchETagHeader != "" {
		if !isETagEqual(objInfo.ETag, ifMatchETagHeader) {

    assertNull(navigableSet.pollLast());
  }

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ONE)
  public void testSingletonSetPollFirst() {
    assertEquals(a, navigableSet.pollFirst());
    assertTrue(navigableSet.isEmpty());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonSetNearby() {
    assertNull(navigableSet.lower(e0()));
    assertEquals(a, navigableSet.floor(e0()));

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *

   * point values. Two instances are guaranteed to be considered equal if one is copied from the
   * other using {@code second = new PairedStatsAccumulator().addAll(first).snapshot()}, if both
   * were obtained by calling {@code snapshot()} on the same {@link PairedStatsAccumulator} without
   * adding any values in between the two calls, or if one is obtained from the other after