code: public @Nonnull
    StringAssert startsWith(@Nonnull String prefix) {
      strings.assertStartsWith(description, actual, prefix);
      return this;
    }
docs: Verifies that the <em>actual</em> {@code String} starts with the given prefix.
  
  @param prefix the given prefix.
  @return {@code this} assertion object.
  @throws NullPointerException if the given prefix is {@code null}.
  @throws AssertionError if the <em>actual</em> {@code String} is {@code null}.
  @throws AssertionError if the <em>actual</em> {@code String} does not start with the given prefix.