/**
  * The duration of the item (movie, audio recording, event, etc.) in <a
  * href='http://en.wikipedia.org/wiki/ISO_8601'>ISO 8601 date format</a>.
  */
 @NotNull
 public Builder duration(@NotNull Duration.Builder duration) {
   putValue("duration", duration.build());
   return this;
 }
 /**
  * Approximate or typical time it takes to work with or through this learning resource for the
  * typical intended target audience, e.g. 'P30M', 'P1H25M'.
  */
 @NotNull
 public Builder timeRequired(@NotNull Duration.Builder duration) {
   putValue("timeRequired", duration.build());
   return this;
 }