This example doesn't implement the callback itself (that could be just a line of code), only the documentation part.

/// tip

The actual callback is just an HTTP request.

	}

	// There are two possibilities:
	// - We use a KMS -> There must be non-empty key ID and a KMS data key.
	// - We use a K/V -> There must be no key ID and no KMS data key.
	// Otherwise, the caller has passed an invalid argument combination.
	if keyID == "" && len(kmsKey) != 0 {
		logger.CriticalIf(context.Background(), errors.New("The key ID must not be empty if a KMS data key is present"))
	}

  }

  /**
   * Returns the <a href="http://mathworld.wolfram.com/CorrelationCoefficient.html">Pearson's or
   * product-moment correlation coefficient</a> of the values. The count must greater than one, and
   * the {@code x} and {@code y} values must both have non-zero population variance (i.e. {@code
   * xStats().populationVariance() > 0.0 && yStats().populationVariance() > 0.0}). The result is not

or for a fee, you must give the recipients all the rights that we gave
you.  You must make sure that they, too, receive or can get the source
code.  If you link other code with the library, you must provide
complete object files to the recipients, so that they can relink them
with the library after making changes to the library and recompiling
it.  And you must show them these terms so they know their rights.

  // This field must only be set by the entity completing the attach
  // operation, i.e. the external-attacher.
  optional bool attached = 1;

  // attachmentMetadata is populated with any
  // information returned by the attach operation, upon successful attach, that must be passed
  // into subsequent WaitForAttach or Mount calls.
  // This field must only be set by the entity completing the attach

    /*
     * The number of used positions in the elements array.  We deduplicate periodically, so this
     * may fluctuate up and down.
     */
    private int length;

    // True if we just called build() and the elements array is being used by a created ISM, meaning
    // we shouldn't modify that array further.
    private boolean forceCopyElements;

    /**

  internal const val B0_FLAG_FIN = 128

  /** Byte 0 reserved flag 1. Must be 0 unless negotiated otherwise. */
  internal const val B0_FLAG_RSV1 = 64

  /** Byte 0 reserved flag 2. Must be 0 unless negotiated otherwise. */
  internal const val B0_FLAG_RSV2 = 32

  /** Byte 0 reserved flag 3. Must be 0 unless negotiated otherwise. */
  internal const val B0_FLAG_RSV3 = 16

0x1.5e-2     // invalid: hexadecimal mantissa requires p exponent
1_.5         // invalid: _ must separate successive digits
1._5         // invalid: _ must separate successive digits
1.5_e1       // invalid: _ must separate successive digits
1.5e_1       // invalid: _ must separate successive digits
1.5e1_       // invalid: _ must separate successive digits
</pre>


<h3 id="Imaginary_literals">Imaginary literals</h3>

				prog.To = a[2]
				break
			}
			if arch.IsARMBFX(op) {
				// a[0] and a[1] must be constants, a[2] must be a register
				prog.From = a[0]
				prog.AddRestSource(a[1])
				prog.To = a[2]
				break
			}
			// Otherwise the 2nd operand (a[1]) must be a register.
			prog.From = a[0]
			prog.Reg = p.getRegister(prog, op, &a[1])
			prog.To = a[2]
		case sys.AMD64:

 *
 * // In case bug 12345 happens again we'd rather just die
 * Verify.verify(bill.status() == Status.UNPAID,
 *     "Unexpected bill status: %s", bill.status());
 * }</pre>
 *
 * <h3>Comparison to alternatives</h3>
 *
 * <p><b>Note:</b> In some cases the differences explained below can be subtle. When it's unclear
 * which approach to use, <b>don't worry</b> too much about it; just pick something that seems
 * reasonable and it will be fine.