The only new thing is the `callbacks=invoices_callback_router.routes` as an argument to the *path operation decorator*. We'll see what that is next.

## Documenting the callback { #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/"

        }

        return type.cast(object);
    }

    /**
     * Gets the next element from an enumeration and casts it to the specified type
     * @param <T> the target type
     * @param type the target class type
     * @param enumeration the enumeration to read from
     * @return next element from enumeration cast to type
     * @throws PACDecodingException if types are incompatible
     */

    assertThrows(
        ConcurrentModificationException.class,
        () -> {
          Iterator<Entry<K, V>> iterator = getMap().entrySet().iterator();
          put(e3());
          iterator.next();
        });
  }

  @MapFeature.Require({FAILS_FAST_ON_CONCURRENT_MODIFICATION, SUPPORTS_PUT})
  @CollectionSize.Require(absent = ZERO)
  public void testPutAbsentConcurrentWithKeySetIteration() {
    assertThrows(

                final DfsReferral start = dr;
                do {
                    final String domain = dr.server.toLowerCase();
                    entry.map.put(domain, new HashMap());
                    dr = dr.next;
                } while (dr != start);

                _domains = entry;
                return _domains.map;
            }
        } catch (final IOException ioe) {
            if (LogStream.level >= 3) {

    this.it = readers;
    advance();
  }

  /** Closes the current reader and opens the next one, if any. */
  private void advance() throws IOException {
    close();
    if (it.hasNext()) {
      current = it.next().openStream();
    }
  }

  @Override
  public int read(char[] cbuf, int off, int len) throws IOException {
    checkNotNull(cbuf);

  @Override
  public boolean hasNext() {
    return delegate().hasNext();
  }

  @CanIgnoreReturnValue
  @Override
  @ParametricNullness
  public T next() {
    return delegate().next();
  }

  @Override
  public void remove() {
    delegate().remove();
  }

    }

    @Override
    public int encode(byte[] dst, int dstIndex) {
        int start = dstIndex;

        // Write context header
        SMBUtil.writeInt4(0, dst, dstIndex); // Next (offset to next context, 0 for last)
        dstIndex += 4;

        SMBUtil.writeInt2(16, dst, dstIndex); // NameOffset (from start of context)
        dstIndex += 2;

   * prev}. {@code ENDPOINT} represents either the first or last entry in the entire map (as
   * appropriate).
   */
  private void setSucceeds(int prev, int next) {
    if (prev == ENDPOINT) {
      firstInInsertionOrder = next;
    } else {
      nextInInsertionOrder[prev] = next;
    }
    if (next == ENDPOINT) {
      lastInInsertionOrder = prev;

/// note

Some response codes (see the next section) indicate that the response does not have a body.

FastAPI knows this, and will produce OpenAPI docs that state there is no response body.

///

## About HTTP status codes { #about-http-status-codes }

/// note

If you already know what HTTP status codes are, skip to the next section.

///

    multiset.add(multiset, 2);
    Multiset<Multiset<?>> copy = SerializableTester.reserialize(multiset);
    assertEquals(2, copy.size());
    assertSame(copy, copy.iterator().next());
  }

  @J2ktIncompatible
  @GwtIncompatible // Only used by @GwtIncompatible code
  private static class MultisetHolder implements Serializable {
    private final Multiset<?> member;