The module "history" is the main module of interest to the end user. It defines class Tag, the key concept in the package, and supplies four functions for creating tags of various sorts. PACT/PDB file users will use a function from module pdb_history instead, but the latter includes the facilities from module history. Therefore, your understanding of the package should begin by reading about module history.
Media are formats for storing time histories. Five are provided in this release, four in module history_medium and one in pdb_history.
Conditions (module history_condition) can be custom-created for expressing complicated conditions for sampling, but this will rarely be necessary given the facilites in class Tag of module history.
Collectors (module collector) are collections of Tags to be managed with a given "clock". Normally only one collector is needed and the standard collector is used, so again this module is rarely of interest to the end user.
Items (module item) are used to describe the quantities to be sampled. Normally Items are created by using the facilities of Tag.