The approach called decomposition into autonomous and comparable blocks specifies a methodology for producing music structure annotation by human listeners based on a set of criteria relying on the listening experience of the human annotator. The present article develops further a number of fundamental notions and practical issues, so as to facilitate the usability and the reproducibility of the approach. We formalize the general methodology as an iterative process which aims at estimating both a structural metric pattern and its realization, by searching empirically for an optimal compromise describing the organization of the content of the music piece in the most economical way, around a typical timescale. Based on experimental observations, we detail some practical considerations and we illustrate the method by an extensive case study. We introduce a set of 500 songs for which we are releasing freely the structural annotations to the research community, for examination, discussion and utilization.