code: @Override
  	public void beforeFirst(SearchRange searchRange) {
  		if (!searchRange.isValid())
  			return;
  
  		search(searchRange, SearchPurpose.READ);
  	}
docs: Traverses the directory to find the leaf page corresponding to the lower
  bound of the specified key range. The method then position the page
  before the first record (if any) matching the that lower bound. The leaf
  page is kept open, for use by the methods {@link #next} and
  {@link #getDataRecordId}.
  
  @see Index#beforeFirst