* supplied by the user of the class. For example, {@code Multiset.Entry.getElement()} returns
 * {@code @ParametricNullness E}, which means:
 *
 * <ul>
 *   <li>{@code getElement} on a {@code Multiset.Entry<@NonNull String>} returns {@code @NonNull
 *       String}.
 *   <li>{@code getElement} on a {@code Multiset.Entry<@Nullable String>} returns {@code @Nullable
 *       String}.
 * </ul>
 *

 * supplied by the user of the class. For example, {@code Multiset.Entry.getElement()} returns
 * {@code @ParametricNullness E}, which means:
 *
 * <ul>
 *   <li>{@code getElement} on a {@code Multiset.Entry<@NonNull String>} returns {@code @NonNull
 *       String}.
 *   <li>{@code getElement} on a {@code Multiset.Entry<@Nullable String>} returns {@code @Nullable
 *       String}.
 * </ul>
 *

 * <p>This tests:
 *
 * <ul>
 *   <li>comparing each object against itself returns true
 *   <li>comparing each object against null returns false
 *   <li>comparing each object against an instance of an incompatible class returns false
 *   <li>comparing each pair of objects within the same equality group returns true
 *   <li>comparing each pair of objects from different equality groups returns false
 *   <li>the hash codes of any two equal objects are equal

   *
   * <ul>
   *   <li>{@link #JAVA_EXT_DIRS} was deprecated in Java 8 and removed in Java 9. We have not
   *       confirmed whether it is available under older versions.
   *   <li>{@link #JAVA_COMPILER}, while still listed as required as of Java 15, is typically not
   *       available even under older version.
   *   <li>Any property may be cleared through APIs like {@link System#clearProperty}.

 * </pre>
 *
 * <p>Here are some examples of recognized formats:
 *
 * <ul>
 *   <li>example.com
 *   <li>example.com:80
 *   <li>192.0.2.1
 *   <li>192.0.2.1:80
 *   <li>[2001:db8::1] - {@link #getHost()} omits brackets
 *   <li>[2001:db8::1]:80 - {@link #getHost()} omits brackets
 *   <li>2001:db8::1 - Use {@link #requireBracketsForIPv6()} to prohibit this
 * </ul>
 *

   * does not include "was cancelled." To be explicit: If this method returns a non-null value,
   * then:
   *
   * <ul>
   *   <li>{@code isDone()} must return {@code true}
   *   <li>{@code isCancelled()} must return {@code false}
   *   <li>{@code get()} must not block, and it must throw an {@code ExecutionException} with the
   *       return value of this method as its cause
   * </ul>
   *

   *
   * <ol>
   *   <li>If {@code index >= end}, {@link IndexOutOfBoundsException} is thrown.
   *   <li><b>If the character at the specified index is not a surrogate, it is returned.</b>
   *   <li>If the first character was a high surrogate value, then an attempt is made to read the
   *       next character.
   *       <ol>

 * </ul>
 *
 * <p>This class is similar to {@link MoreExecutors#newSequentialExecutor}. This class is different
 * in a few ways:
 *
 * <ul>
 *   <li>Each task may be associated with a different executor.
 *   <li>Tasks may be of type {@code AsyncCallable}.
 *   <li>Running tasks <i>cannot</i> be interrupted. (Note that {@code newSequentialExecutor} does

 * that wrap {@link MessageDigest}s.
 *
 * <p>Parameters for the benchmark are:
 *
 * <ul>
 *   <li>size: The length of the byte array to hash.
 *   <li>algorithm: the algorithm to hash with (e.g. MD5, SHA1, etc.).
 *   <li>hashMethod: how to hash the data (using the Hashing API or the MessageDigest API).
 * </ul>
 *
 * @author Kurt Alfred Kluever
 */

  /**
   * Determines whether two possibly-null objects are equal. Returns:
   *
   * <ul>
   *   <li>{@code true} if {@code a} and {@code b} are both null.
   *   <li>{@code true} if {@code a} and {@code b} are both non-null and they are equal according to
   *       {@link Object#equals(Object)}.
   *   <li>{@code false} in all other situations.
   * </ul>
   *