The reference states what the toolchain accepts and what it does — exactly, with every value spelled the way the compiler spells it. Where the capability catalog explains what the compiler guarantees and why, the reference is the part you consult with a command line open.

It grows chapter by chapter alongside the release train:

ChapterCovers
The command lineevery flag of the mica binary: modes, inputs, targets, optimization, deployment classes, diagnostics
Traps and tiersevery runtime trap by name, the tier each one runs on, and what each optimization tier proves, guards, and deliberately leaves undefined
Library contractsthe mica.external format whole: libraries, link blocks, types, functions, encodings, and the error conventions the compiler lifts
The type systemevery type kind and the capabilities it carries, what promotion does implicitly and a cast does explicitly, and the rules that read capabilities rather than names
Known limitationswhat the current release deliberately does not do, the spelling that works instead, and where each boundary is headed
The languagein preparation — the language reference arrives as its own set of chapters