code: public <T extends Widget & Checkable> boolean check(T checkableWidget) {
          if (hasChild(checkableWidget)) {
              return checkInternal(checkableWidget, true);
          }
  
          return false;
      }
docs: Set the specified {@link Checkable} {@link Widget} as checked, if it is a child of this
  {@link CheckableGroup} and not already checked.
  
  @param checkableWidget The {@code Checkable Widget} to
  {@linkplain Checkable#setChecked(boolean) set checked}.
  @return {@code True} if {@code checkableWidget} is a child of this {@code CheckableGroup} and
  was not already checked; {@code false} otherwise.