The IEEE Taxonomy comprises the first three hierarchical 'levels' under each term-family (or
branch) that is formed from the top-most terms of the IEEE Thesaurus. In this document these
term-families are arranged alphabetically and denoted by boldface type. Each term family's
hierarchy goes to no more than three sublevels, denoted by indents (in groups of four dots)
preceding the next level terms. A term can appear in more than one hierarchical branch and
can appear more than once in any particular hierarchy. The IEEE Taxonomy is defined in this
way so that it is always a subset of the 2020 IEEE Thesaurus.