Modular

undefined:

Modular systems (or layers, sidesystems, subsystems, etc.) have fragments (described "autonomous ego functions" ) that "merge", "stack", or "combine" together situation-by-situation to create temporary system members that afterwards "break apart". Those system members often come off as vague and may not been seen in the same way again, or only in the same specific circumstance.

A common analogy is Lego bricks: each fragment can be represented by a separate brick, which assemble to create someone on the fly. The system member is then easily disassembled and the bricks exist separately once more.

Typically, modular systems do this process unconsciously, but some have some sort of assembler that guides this process.

History
Modular Dissociative Identity Disorder was first described by Richard Kluft in a paper titled Clinical Presentations of Multiple Personality Disorder. In his experience, this form is associated with severe trauma, creativity, and knowledge of computers. It is listed separately from polyfragmented DID and other presentations, some of which have more modern relevance than others. (A more accessible and simplified list of Kluft's noted presentations is available here.)

Related Terms
Modular systems can be compared to polyfragmented ones, as they both possess large amounts of fragments and additional complexity compared to "standard" presentations.