A data structure that includes border data structures that appear at the respective interfaces between each of at least some of the segments in the data structure. The border does not conform to a data format for any of the elemental data types of the elemental data items represented within the data structure, and does not represent a size of any of the neighboring segments. Second, the data structure also includes an index. When writing the data structure, the writer tracks the position of each of the regions. When all segments and regions have been written, the writer can then write an index that represents the position of each region. The reader can then use that index to quickly read from only those regions of interest, and quickly skip over regions not of interest.