code: public MeasureMap putAttachment(String key, AttachmentValue value) {
      // Provides a default no-op implementation to avoid breaking other existing sub-classes.
      Utils.checkNotNull(key, "key");
      Utils.checkNotNull(value, "value");
      return this;
    }
docs: Associate the contextual information of an {@code Exemplar} to this {@link MeasureMap}.
  Contextual information is represented as a {@code String} key and an {@link AttachmentValue}.
  
  <p>If this method is called multiple times with the same key, only the last value will be kept.
  
  @param key the key of contextual information of an {@code Exemplar}.
  @param value the value of contextual information of an {@code Exemplar}.
  @return this
  @since 0.20