A block design is t-wise balanced if each set of distinct points is contained in a constant number of blocks; it does not imply constant block size. (The two properties together specify a -design.) Unlike for -designs, a block design may be -wise balanced but not -wise balanced for . We store information about the values of for which the design is -wise balanced as list of index_flags.
Here is an example of the t_wise_balanced element for the Fano plane:
<t_wise_balanced> <index_flag flag="true" index="1"> </index_flag> <index_flag flag="true" index="2"> </index_flag> </t_wise_balanced>