Layer

Purpose

One layer of a stack — a domain with its own vocabulary, holding the drafts that speak it. In the published trees a layer is what a crate's drafts describe: convene's "core" is Anne and Laura's comms domain, its "mix" is the team's transport domain, and this site's "atlas" is the layer you are reading now. Within a layer every name is spoken for exactly once — two drafts bearing the same name would leave a mention with no honest target, so the layer refuses them.

Attributes

• name: is Text that the layer goes by
• drafts: is every Draft that it holds

Invariants

• No two drafts bear the same name — a layer holding two drafts of the same name is rejected.

Operations

named

Reports the Draft, if any, bearing a given name Text — nothing when no draft here bears it. Result: the Draft, if any

Scenarios

A layer holds its drafts

Given: a Draft named "Cell" and a Draft named "Tumbler", both of the layer "mix" When: a Layer named "mix" is created with them Then: it is accepted, and named "Cell" yields the Cell draft while named "Tumbler" yields the Tumbler draft

An unknown name reaches nothing

Given: a Layer named "mix" holding a Draft named "Cell" When: named is performed with "Seal" Then: nothing is yielded