bookspec: examples (seed)

bookspec is the formal accounting specification planned in plan/served.md (P13, D-34): every rule stated normatively, sourced to its authority, with a symbolic form and concrete examples, independent of any engine. Its own repository comes later. Until then this directory holds its first examples: P3's regression tests, each written here as it is built, so the spec starts from cases a real engine got wrong.

Every example is checked against wanderbooks on every cargo test (crates/ledger-core/tests/bookspec.rs, and for the formats appendix crates/ledger-package/tests/package.rs): an example the engine disagrees with fails the build, so the examples can't rot. An expected value is worked by hand from the cited source, never copied from an engine's output.

The shape of an example

One TOML file per example in examples/, named for its id.

id = "cash-flow.reversed-property-contribution"   # stable; never reused
title = "A property contribution reversed the same day"
rule = "One normative sentence: what MUST (or MUST NOT) hold."
status = "AUTHORITY"            # AUTHORITY | CONVENTION | CHOICE
sources = ["ASC 230-10-45-24", "ASC 230-10-50-3"]   # exact citations
tags = ["accrual", "book", "us"]                     # applicability

[setup]
currency = "USD"                # ISO 4217
fiscal_year_start = "01-01"     # MM-DD
basis = "accrual"               # accrual | cash
rounding = "half-even"          # half-even | half-away-from-zero |
                                # largest-remainder: how a figure is
                                # rounded to the currency's minor unit,
                                # where a rule rounds (none here)

[[setup.accounts]]
code = "1000"
name = "Cash"
type = "asset"                  # asset | liability | equity | revenue | expense

[[events]]                      # in order, counting from 1
date = "2026-01-10"
description = "Property contributed"
lines = [
  { account = "1500", side = "debit", amount = "2340.00" },
  { account = "3000", side = "credit", amount = "2340.00" },
]

[[events]]
date = "2026-01-10"
description = "Reverse entry 1"
reverses = 1                    # the event (1-based) whose entry this
                                # one reverses: its lines, sides flipped;
                                # no `lines` here

[[expect]]
query = "cash_flow"             # what is asked of the books (see below)
from = "2026-01-01"             # inclusive
to = "2026-12-31"               # inclusive (a query as of a day: as_of)

[expect.values]                 # every value an exact decimal string
operating = "0.00"

Events count from 1: the first [[events]] is event 1. An event is an entry (lines), a reversal (reverses), a close (close, below), a bill or an invoice (bill, invoice, below), each posting one entry; or one of the books' commands that post what is due (run_depreciation, dispose_asset, run_schedules, below), which post as many entries as are due, none included; or a schedule's registration (register_schedule), which posts none: exactly one of them. A key that names an event (reverses = N, entry = N, a cash flow's <N>) names the entry event N posted, one before it: an event that posted none, or several, can't be named that way, and reverses = 0 names no event and is refused. While every event posts one entry, event N's is entry #N. A change that posts no entry (a rename, a policy) is a [[changes]] entry instead (below). A key the shape doesn't have is refused too, never ignored.

An entry, a reversal, a close, a bill, an invoice and a disposal are dated (date); the other commands date their own entries (a run its month's end) and take no date. An entry, a reversal, a close, a bill and an invoice are described (description); a command describes its own entries and takes none.

The books are the engine's own (ledger_store::Store, in a directory of their own): each event is the command the books take it by, journaled as they journal it, and after every expectation is checked the books must replay to what they kept (Store::verify).

rounding names the rule the example's figures are rounded by where one rounds: half-even or half-away-from-zero to the currency's minor unit, or largest-remainder for an amount split among parts (each part rounded down, the units left over to the largest remainders, ties to the part listed first; rules.md B-13). An example that closes to the members declares largest-remainder, the rule a members close splits by.

status says what the expected values rest on: AUTHORITY, the cited authorities alone (a standard, a regulation, a statute, a court, the mechanics of double entry); CONVENTION, common practice where no authority governs (rules.md's CONVENTION); CHOICE, an owner's or the house's decision (a plan D-number, or a DECISION rules.md records) that some expected value depends on, even when authorities carry the rest. An example whose figures follow a decision cites it in sources.

Required everywhere: the top-level keys (title, rule, tags and sources non-empty), [setup] with its four keys and its accounts, the events (events = [], before [setup], when nothing is posted), and at least one [[expect]]. A value from a closed list (a type, a kind, a role, a form, a basis) is spelled exactly as written here. A figure query's values are exact decimal strings ("2340.00", "-12.50"; never a float), a format query's are text (below). Amounts on lines are positive; the side gives the direction.

Optional keys, for the rules that need them

• appendix = "formats" (top level): the example shows an interchange format, not an accounting rule (P13's appendix of formats; the IIF file today). It loads like any other; only it may ask a format query.

• parent on an account: its parent account's code. A parent is declared before its subaccounts.

• header = true on an account: a header, which groups other accounts and takes no postings (it needs no tax category: rules.md B-32).

• tax_category on an account: its tax category, a key of the books' catalog (gross_receipts, office_expense, ...; ledger_core::tax), its link to a line of the return (B-32).

• today (in [setup]): the day the books are asked on, YYYY-MM-DD, in the company's time zone: what an omitted date means (B-30). A query that omits a date needs it.

• cash_accounts, financing_accounts, investing_accounts (in [setup]): arrays of account codes, the statement of cash flows' account roles (ASC 230-10-45-10 to 45-15). The cash and financing accounts are also what a payee is paid from, for vendor_1099_paid and vendor_1099 (a payment card is neither: its charges go on Form 1099-K; rules.md B-19); with the cards, what party money is, for party_part and party_totals (B-35 item 5: no cash_accounts, every asset account but receivables); the cash accounts are what the K-1 worksheet reads as money (k1, k1_tax_basis, k1_reconciliation) and an IIF file's bank accounts (B-34).

• [[setup.fixed_assets]] { cost_account, accumulated_account, expense_account }: accounts that hold property and equipment (their cost and accumulated depreciation are investing; ASC 230-10-45-12(c), 45-13(c)), for an example no asset's own figures matter to. An asset with its figures is a [[setup.assets]] entry (below), whose accounts hold property and equipment too.

• [[setup.assets]]: fixed assets registered before the first event, each named by its id in the events and queries that ask about it (rules.md B-15):

  [[setup.assets]]
  id = "X"                      # its name in this example
  description = "Asset X"
  cost = "12000.00"
  salvage = "0.00"
  life_months = 12
  in_service = "2026-01-01"     # depreciation starts here
  method = "straight_line"      # the one method the books have
  cost_account = "1500"
  accumulated_account = "1510"
  expense_account = "6200"
  acquired_by = 2               # optional: the event whose entry put it
                                # on the books (B-15 rule 7)
  basis = { rule = "personal_use_conversion",
            contributor_adjusted_basis = "1688.40",
            fmv_at_contribution = "1440.00",
            sec704c_method = "traditional" }   # optional (B-25)
  

  Registering an asset posts nothing: the entry that buys it is an event of its own. acquired_by = N links that entry, event N's, once the event is applied: its date is the asset's acquired date, which puts it on the register (before it, the in-service date does). basis records how the company got it and the facts its tax figures follow from, as the asset is registered: rule "purchase", "carryover_723" or "personal_use_conversion"; a contribution's contributor_adjusted_basis and fmv_at_contribution; the §704(c) method if chosen ("traditional", "traditional_with_curative", "remedial").

• [[setup.schedules]], and register_schedule = { ... } as an event: a prepaid expense or deferred revenue recognized over its months (rules.md B-16), named by its id: { id, kind, description, total, start, months, convention, balance_account, pl_account }, kind "prepaid_expense" or "deferred_revenue", convention "daily" (by the day, the last month taking what the others leave) or "monthly_even" (equal months from the 1st). Registering one posts nothing.

• [[setup.parties]] { name, roles, creditor_of?, tin_last4?, w9_tin_last4?, tin_purged? }: the company's directory (B-26). roles are role keys (member, vendor, customer, contractor, landlord, employee, financial_institution, payout_platform, tax_agency, government_agency); vendor or customer (one at most) gives the party its record. creditor_of: the liabilities, by code, the company owes the party itself (a card's issuer, a lender, each member for what the members advanced: B-35 item 6). tin_last4: its TIN facts' last four (an SSN's); w9_tin_last4: its W-9's (a 1099 role's); tin_purged = true: the vault's copy purged, the facts kept (needs tin_last4). Never a full TIN. Each name once.

• [[setup.members]] { name, capital_account, share?, distributions_account? }: the members of a multi-member LLC. share is the member's share of income, an exact decimal fraction above zero ("0.5", "0.3333"); every member has one or none does, and the shares sum to

  1. A close to the members, members_equity, k1, k1_tax_basis and k1_reconciliation need them. distributions_account: the member's distributions account (B-13). A member whose name is a party's in setup.parties with the member role is that party, as the company's settings name them: an entry's parties' shares resolve with those members (B-35), and so does the 1099 worksheet.

• [[setup.payees]] { name, form }: a payee marked for an information return from the beginning, form "1099-NEC" or "1099-MISC"; each name once. A payee in setup.parties with the vendor role is that party's vendor record; any other is a vendor record of its own.

• [[setup.status_changes]] { payee, effective, decision, reason_kind?, reason? }: a payee's 1099 decision from effective (YYYY-MM-DD) on (rules.md B-19, D-40: an LLC's corporate election, say): decision "1099-NEC", "1099-MISC", "undetermined" or "not_reportable", the last with reason_kind (corporation, tax_exempt, united_states, state, foreign_government, foreign_person, merchandise, employee, other) and the facts in words (reason). Each payment takes the decision in force on its date.

• [[setup.instruments]] { label, kind, account, last4?, owner? }: a payment method (B-19): kind bank, business_card, member_card, member_cash_or_check or platform; account the code it pays through; owner a party's name in setup.parties (informational); each label once. A business card's liability is a card account (B-35 item 5): while none is recorded, a liability whose name says "card", not "gift card", is.

• [[setup.projects]] { name, kind?, status?, party? }: a project (rules.md B-37), added with its facts, each name once: kind internal, client, on_spec or other; status active (the default), paused, finished or abandoned; party a setup.parties name.

• project = "<name>" on a line of lines: the line is tagged with that project (a setup.projects name), as the books' command tags it, after the line is added. Not on a reversal, which carries its original's tags.

• payee on an event: the payee (by name, one of setup.payees) the entry paid. Only on an entry (lines): a reversal takes its original's, a bill names its vendor, an invoice its customer, a close and a command have none.

• parties = [{ party, amount? }, { party, percent? }, ...] on an event: the parties (by name, in setup.parties) the entry is with, each with its share: an amount (an exact decimal string), a percent, or neither (derived from the entry: all of it for one party, the members' capital lines or income shares for several: B-35). An entry naming a party with a vendor record is tagged with that payee too; with payee as well, the payee's party is one of the parties.

• instrument on an event: the payment method (a setup.instruments label) the entry was paid with. Neither parties nor instrument on a reversal, which takes its original's, nor on a command.

• close = { start, to, rounding? } as an event: closes the period from start through the event's date (rules.md B-11, B-13), to "members" (split by share, in the order listed) or "retained_earnings". A close to the members splits cumulatively, each close giving each member their split of everything the members' closes have closed less what earlier closes gave them; rounding = "per-close" (members only) splits that close's net on its own instead (books from an engine that rounded each close by itself). A close must have something to close: it posts one entry like any other event.

• bill = { vendor, amount } or bill = { vendor, lines = [{ amount, description?, project? }, ...] } as an event: a bill from vendor (a name; a payee's record if one has it) for amount (one line, described as the event) or its lines (exactly one of them; a line's description is the event's when left out), dated and due on the event's date. It posts one entry: General Expenses (6999) debited and Accounts Payable (2000) credited, each account created with that fixed name when first needed, as the books create a control role's account (B-32). A line's project (a setup.projects name) puts its cost on that project: the entry's expense side is one line per project named, the untagged lines' as one, the payable line never tagged (B-37 item 8).

• invoice = { customer, amount } or invoice = { customer, lines = [...] } as an event: an invoice to customer (a name, its record added when first named), as a bill is (the same lines), dated and due on the event's date. It posts one entry: Accounts Receivable (1200) debited and Revenue (4000) credited, each created with that fixed name when first needed; a line's project puts its revenue on that project, the receivable line never tagged (B-37 item 8).

• run_depreciation = { asset, period } as an event: the asset's run for period ("YYYY-MM"), which posts what the schedule says is due through the month's end and the books don't carry, dated then: a skipped month caught up, nothing when nothing is due (rules.md B-15).

• dispose_asset = { asset, proceeds, proceeds_account, gain_loss_account } as an event, dated: the asset's disposal for proceeds (an exact decimal, zero allowed), received into proceeds_account, its gain or loss to gain_loss_account (B-15). It posts the depreciation still due through its day in an entry of its own when the month has no run, then the disposal entry.

• run_schedules = { through } as an event: every schedule's months due through through posted (B-16).

• refused = "<reason>" on a reversal or a command: the books refuse it, for that reason (below); it changes nothing, posts nothing, and the example goes on without it.

• [[changes]] { after, rename?, require_tax_category?, correct_asset? }: a change that posts no entry, exactly one of rename = { code, name } (rename the account code, B-31), require_tax_category = "warn" or "refuse" (the policy, B-32; the books start at warn) and correct_asset = { asset, cost?, salvage?, life_months?, in_service?, reason } (a registration mistake corrected: each figure given replaces the asset's, the rest stay; refused while the books carry depreciation for it). It is made right after event after (1 to the number of events), once the expectations asked after that event are checked, in the order listed.

• after = N on an expectation: asked of the books after event N (before the changes made after it), not after the last event and every change (1 to the number of events; not on a format query).

Party totals and the 1099 worksheet answer different questions (B-35 item 9): a member paying a contractor through the members' financing account is, in party totals, paid to the contractor (money, the members' financing being money) and nothing to the member until the company reimburses them; on the 1099 worksheet it is the company's payment, counted toward the contractor's 1099 unless it was made by card (B-19), and undetermined until its payment method is recorded.

Queries and their values

A query over a period takes from and to; a query as of a day takes as_of; the other is refused. A date left out is resolved by the one rule (rules.md B-30) on setup.today: an omitted to is today, an omitted from the first day of the fiscal year that holds to, an omitted as_of today (vendor_1099_paid, vendor_1099, party_totals and the format queries give theirs). A query no crate answers is refused, never skipped.

query	dates	values	checked by
cash_flow	from, to	figures (below)	ledger-core tests/bookspec.rs
trial_balance	as_of	each account's balance by code, debits less credits (a credit balance negative), every account of setup.accounts listed (not those the books create)	ledger-core tests/bookspec.rs
profit_and_loss	from, to	each revenue and expense account's activity by code, on its normal side, closing entries left out, every one of setup.accounts listed; net_income, revenue less expenses	ledger-core tests/bookspec.rs
entry	entry = N, no dates	the lines of event N's entry, "<code>.debit" and "<code>.credit" each the sum of that account's lines on that side, every line of the entry named	ledger-core tests/bookspec.rs
balances	as_of	each account named by code, its balance on its normal side (a member's capital after a loss is negative); the example names the accounts it shows	ledger-core tests/bookspec.rs
members_equity	from, to	the statement of changes in members' equity (rules.md B-13): "<member>.beginning", .contributions, .net_income, .distributions, .other, .ending; the example names the figures it shows	ledger-core tests/bookspec.rs
k1	from, to	the K-1 worksheet (B-13; Schedule K-1 Item L): "<member>.beginning", .contributions_cash, .contributions_property, .net_income, .distributions, .other, .ending; the example names the figures it shows (cash_accounts required)	ledger-core tests/bookspec.rs
k1_tax_basis	from, to	the K-1 worksheet on the tax basis (B-36; Schedule K-1 Item L, tax-basis method), beside k1's book figures: "<member>.beginning", .contributions_cash, .contributions_property, .net_income, .other, .distributions, .ending; a line the books can't know is "open", with what they know so far as "<member>.known_<line>"; the example names the figures it shows (cash_accounts required)	ledger-core tests/bookspec.rs
k1_reconciliation	from, to	each member's book capital less tax-basis capital at to, by cause (B-36): "<member>.beginning", .built_in_gain_704c, .property_without_basis, .property_distributed, .total; the example names the members it shows, each with every cause (cash_accounts required)	ledger-core tests/bookspec.rs
vendor_1099_paid	from (January 1 of to's year), to	each payee's payments that count toward its 1099, by name: out of the cash and financing accounts (cash_accounts required), a card's or payment network's left out (B-19), every payee listed	ledger-core tests/bookspec.rs
vendor_1099	payee; from (January 1 of to's year), to	one payee's line of the 1099 worksheet (B-19): status (reportable, under_threshold, not_reportable or undetermined), threshold, paid (counts toward its 1099), excluded_card (a card's or payment network's: Form 1099-K), undetermined (through a financing account, its payment method not recorded), not_reportable (paid while decided not reportable), every one given	ledger-core tests/bookspec.rs
party_part	entry = N, party, no dates	entry N's part for the party (B-35): resolved, signed as a line on the party's own account would be (paid or given positive, received negative), the entry's direction (paid, received or neither), and what of it moved as money (cash) and as property (in_kind), every one given	ledger-core tests/bookspec.rs
party_totals	party, basis (cash or all), from, to	what was paid to the party and received from it over the period (B-35 item 4: basis cash money, all money and property in kind; each entry on its first original's side), both given	ledger-core tests/bookspec.rs
party_tin_last4	party, no dates	tin_last4: the party's TIN facts' last four, else its W-9's, "" for none (B-26)	ledger-core tests/bookspec.rs
period	from, to, either or both left out	the dates a period report asked with those dates covers, by the one rule (B-30): from, to (YYYY-MM-DD); or refused	ledger-core tests/bookspec.rs
day	as_of, or left out	the day a report as of a day is made as of: as_of	ledger-core tests/bookspec.rs
calendar_year	none	the year a calendar-year count (1099s, party totals) asked without one counts: year	ledger-core tests/bookspec.rs
account_names	none	each account's name by code, as the chart holds it and every report prints it, past periods included (B-31); every account listed, those the books created included	ledger-core tests/bookspec.rs
uncategorized_accounts	none	a list: every account that needs a tax category (revenue or expense, not a header) and has none, with activity or not, "<code> <name>", by code (B-32)	ledger-core tests/bookspec.rs
run	event = N, no dates	what the run_depreciation event N posted: amount (zero when nothing was due, or the month had its run already), and caught_up, what of it is beyond the month's own depreciation (B-15); both listed	ledger-core tests/bookspec.rs
disposal	asset, no dates	what the asset's disposal took (B-15), every figure listed: final_depreciation (posted in its own entry), catch_up_depreciation and excess_depreciation (charged, and credited back, in the disposal entry), accumulated (cleared), book_value, gain_loss (a gain positive)	ledger-core tests/bookspec.rs
depreciation_schedule	asset, as_of	the asset's schedule through the day (B-15): each month named ("YYYY-MM") its depreciation, "0.00" for a month it doesn't reach; accumulated and book_value through the day; the example names the figures it shows	ledger-core tests/bookspec.rs
register_row	asset, as_of	the asset's row of the fixed asset register (B-15 rules 7 and 8, B-24): acquired, in_service (YYYY-MM-DD), cost, accumulated_scheduled (the schedule's), accumulated_posted (what the books carry), unposted (the one less the other), book_value (cost less posted), each "0.00" once disposed; the example names the figures it shows; an asset acquired after the day is refused	ledger-core tests/bookspec.rs
register_totals	as_of	the register's totals over the assets held (B-24, B-25): total_cost, total_accumulated_scheduled, total_accumulated_posted, total_book_value, total_depreciable_basis, total_tax_basis_723, missing_basis (a count), and how it ties to the books: unregistered_cost, unposted_depreciation, unattributed_accumulated; the example names the figures it shows	ledger-core tests/bookspec.rs
asset_basis	asset, no dates	the asset's basis facts and the tax figures they give (B-25): rule, contributor_adjusted_basis, fmv_at_contribution, tax_basis_723, depreciable_basis, built_in_gain_704c (a loss negative), each "none" where it has none, and sec704c_1c ("true" for a built-in loss, which counts only for the contributor); the example names the figures it shows	ledger-core tests/bookspec.rs
project	project, from, to	the project's figures (B-37), every one given: revenue, expenses and net for the period (the revenue and expense lines tagged to it, closes left out), to_date.revenue, to_date.expenses and to_date.net (every tagged line through to), and unrecovered_cost (expenses less revenue to date, never below zero; "none" unless it is on spec)	ledger-core tests/bookspec.rs; ledger-mcp project_figures_match_profit_and_loss_by_class
schedule_plan	schedule, no dates	the schedule's plan (B-16): what it recognizes at each month end named ("YYYY-MM-DD"), "0.00" at one it doesn't post; total, all it recognizes; the example names the figures it shows	ledger-core tests/bookspec.rs
iif_lines	as_of	formats appendix: the file's lines in order, each its fields joined by tabs, without the CR LF that ends each	ledger-package the_bookspec_iif_example_matches_the_engine
iif_changes	as_of	formats appendix: each text the file writes differently from the books, in file order, as [what, books' text, file's text] (the example's header gives what)	ledger-package the_bookspec_iif_example_matches_the_engine

A figure query is a table ([expect.values], or values = { ... }); a format query, and uncategorized_accounts, an array (values = [ ... ]). period, day and calendar_year give dates and a year, account_names names, party_part's direction, vendor_1099's status and party_tin_last4 words, not figures; register_row gives dates beside its figures, project gives "none" as the unrecovered cost of a project that isn't on spec, asset_basis a rule's name, "none" and "true" or "false", and a k1_tax_basis line "open", beside them.

A command is tried on a copy of the books, as the books' own command does it, and changes nothing checked after it. It shows no values: it is accepted = true, or refused = "<reason>".

command	keys
rename_account	code, name	rename the account (B-31); accepted, it must move no amount and keep the name trimmed
add_account	account = { code, name, type, parent?, header?, tax_category? }	add the account, under the policy in force (B-31, B-32)
set_tax_category	code, category (left out: clear it)	set or clear the account's tax category, under the policy in force (B-32)

A refusal (a command's, or a period's) is named for what was refused, never by an engine's message: end_before_start (both dates given, the start after the end), start_after_today (only a start, after today, the end an omitted end means), blank, unchanged (the name the account has, trimmed), sibling_has_it (another account under the same parent has the name, ignoring capitals and surrounding space), holds_a_tin (a run of nine digits), not_one_line (a line break, tab or other control character, or past 200 characters), code_taken, and tax_category_required (an account that needs a category left without one under refuse). A refused event's: depreciation_past_disposal (a disposal dated before depreciation a run carries: a later month's run stands, or a run's change dated after the disposal's month isn't undone), entry_irreversible (an asset's entry that can't be reversed: its disposal, a disposed asset's depreciation, a run re-instated twice or past its schedule, or a reversal dated before its run), already_disposed, invalid_depreciation_period (a month that ends before the asset is in service) and invalid_schedule (an equal-months schedule not starting on the 1st, among others).

cash_flow (rules.md B-14): the statement of cash flows for [from, to].

key	the value
operating, investing, financing	each section's net cash, + in
net_change, cash_beginning, cash_ending	the cash accounts' change and balances
difference	sections less the change in cash: always "0.00"
net_income	revenue less expenses, closing entries excluded
<section>.<N>	event N's entry's cash in that section (financing.4)
<section>.<N>.on_behalf	of it, what a member or a lender paid or received for the company, no cash account moving (constructive receipt and disbursement)
<section>.count	how many entries the section lists
class.<a..g>	an operating class's total, by ASC 230-10-45-25's letter: (a) from customers, (b) interest and dividends received, (c) other receipts, (d) paid to suppliers and employees, (e) interest paid, (f) income taxes paid, (g) other payments; given one, every class the statement has must be given
noncash.<N>	event N's entry's noncash investing and financing disclosure
noncash.count	how many entries are disclosed
reconciliation.depreciation	depreciation added back
reconciliation.investing_gain_loss	gains and losses whose cash is investing, taken out
reconciliation.noncash_through.<code>	operating movements no cash settled, through that account
reconciliation.other_noncash	other operating movements no cash settled
reconciliation.balance_change.<code>	minus the change in an operating asset or liability

An entry named in a <section>.<N> (or .on_behalf) or noncash.<N> key must be the only such entries when <section>.count or noncash.count is given too; a reconciliation key not given must be zero or absent.

Every example, in any appendix, is loaded by crates/ledger-core/tests/bookspec.rs (every_bookspec_example_holds): its shape (a key the shape doesn't have is refused), its setup, and every event taken or refused as it says, on the books' own store. Each query is then checked by the crate that answers it (the table above), so the shape never rots either.

Licence and sources

The examples state rules in their own words with the paragraph cited (FASB's Codification is copyrighted: cited, never copied; see docs/spec/sources/fasb-asc.md). The examples are MIT OR Apache-2.0, as the rest of this repository, until bookspec moves to its own repository (planned: the spec under CC BY 4.0).