An engineer develops a sparse attention mechanism where, for any given token, the set of other tokens it can attend to is defined by a pre-determined, structured pattern based on their relative distance in the sequence. For example, a token might only attend to the 8 tokens immediately preceding it. This attention pattern does not change, regardless of the specific words or meaning of the input text. Based on how the set of attended-to indices is defined, how should this mechanism be classified?