MAPT and tauopathy: In addition to the division into primary (where tau is considered the sole and/or primary mediator of neurodegeneration) and secondary (where tau coexists with other pathology) forms, disease‐specific signatures for each tauopathy exist based on which cell types bear inclusions (neurons, glia, or both), their morphological appearances and anatomic distribution, and the ratio of 3R:4R tau.3, 6