bdeshi
f4ba695e87
A pass over the content at startup writes three widths per picture into a cache outside the site root, named by the source's content hash and the width (ADR-0042). Idempotent by construction: a rerun stats and skips, an edited picture takes a new name, and nothing stale can be served under an old one. Restarting the evidence site made 0 derivatives the second time, as it should. Ahead of the request rather than during it, because resampling is felt and there is no page cache yet to hide it. Outside the site root, because the engine reads that directory and must not leave generated files in somebody's content git — a lost cache costs one startup pass and no correctness. Markup now carries the original as src, the derivatives as srcset closed by the original at its own width, and width/height from the original — which retires most of the latent row about the output floor; only a gallery's alt is still empty, and a filename cannot supply that. Two things the work itself decided: `Fragment.Items` became `Fragment.Pictures`, ADR-0037's own revisit trigger. Items had one consumer, so widening it beat adding a second list beside it. "A browser can show it" and "we can resample it" are different questions, and conflating them nearly deleted content: an SVG has no decoder here, so a single predicate would have dropped SVGs from galleries silently. Undecodable and unsupported pictures are now rendered as they are, without a size or a srcset.
201 lines
12 KiB
Markdown
201 lines
12 KiB
Markdown
# Theme contract
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What the engine promises a theme, and the only thing this repository is bound to (ADR-0023). A theme's
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markup, layout and styling are not the engine's business; a theme's *inputs* are.
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**STATUS: partly live.** The fields under *Live today* exist and are gated; everything else is the shape
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the contract takes when the feature arrives. All of it is engine obligation, not theme instruction — a
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theme may ignore any of it.
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## Live today
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A bundle page receives:
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| Field | Contents |
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| `.Title` | may be empty; a template falls back to `.Key` rather than failing |
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| `.Lang` | the locale of this variant, always set |
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| `.Key` | the bundle's identity, without language or extension. **Not its address** — a `slug` moves the address and leaves the key alone, so link with `.URL` or `.Canonical` and never by assembling a key (ADR-0035) |
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| `.HTML` | the rendered body, already escaped |
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| `.Extra` | every frontmatter key the parser does not name (ADR-0002) |
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| `.Style` | the reference theme's stylesheet, inlined so a bare site root needs no asset route |
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| `.Canonical` | the permalink of the variant actually served — not the URL requested, which differs when the fallback chain supplied another language. **Absolute** when the site declares `base`, since a canonical link is resolved by machines rather than by the page (ADR-0039) |
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| `.Alternates` | every language this key exists in, as `.Lang` and `.URL`, for `hreflang`. Absolute on the same terms |
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| `.Site` | what the site declared about itself: `.Site.Base` and `.Site.Title`, either possibly empty |
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| `.Sequence` | the series this page sits in, absent when it sits in none (ADR-0033) |
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`.Sequence` carries the reading order and this page's place in it:
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| Field | Contents |
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| `.Sequence.Title`, `.Sequence.URL` | the series' title (may be empty) and its permalink |
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| `.Sequence.Members` | every entry in reading order, each as an `.Items` entry — *ascending*, unlike a dated listing |
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| `.Sequence.Index`, `.Sequence.Count` | this page's 1-based position and the total; `Index` is 0 when this page is the series landing itself |
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| `.Sequence.Prev`, `.Sequence.Next` | the neighbours, absent at the ends and on a landing page. `Prev` is the **earlier** entry — the opposite sense of a listing's `.PrevURL` |
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| `.Sequence.First`, `.Sequence.Last` | the ends of the series, present whenever it has members |
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A landing page therefore renders an archive from `.Members` and a chapter renders navigation from
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`.Prev`/`.Next`, both from one field. Membership and order are the engine's business
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(`content-model.md`); a theme never sorts.
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Two named templates: `base` is executed for every page; `main` is the block each kind of page defines and
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a theme redefines. There is one parsed set per kind — bundle and listing today — so two kinds may both
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define `main` without colliding (ADR-0019).
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A listing page receives `.Title`, `.Lang`, `.Canonical`, `.Style` as above, plus:
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| Field | Contents |
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| `.Items` | entries on this page: `.Title`, `.Key`, `.URL`, `.Date` |
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| `.Page`, `.Pages` | 1-based position and total, `Pages` at least 1 |
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| `.PrevURL`, `.NextURL` | empty at the ends; *newer* is `prev`, because the order is newest first |
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| `.Groups` | set instead of `.Items` when entries are grouped — a tag listing groups by section, each `.Name` and `.Items` |
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## Chrome text and formatting
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Three functions, available in every template including a site root's own blocks. They exist so no template
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hardcodes English: the words the engine supplies are the engine's to localise (ADR-0034).
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| Call | Gives |
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| `{{t .Lang "newer"}}` | one phrase in that language. Extra arguments fill `%s` placeholders in order |
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| `{{num .Lang .Page}}` | an integer in that language's digits — `12`, `১২` |
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| `{{day .Lang .Date}}` | a date as that language reads it — `8 March 2026`, `৮ মার্চ ২০২৬`; empty for a zero date |
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Phrase keys today: `newer`, `older`, `empty`, `page-of` (two arguments), `position` (two arguments). An
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unknown language falls back to the default locale and an unknown key returns itself, so a missing
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translation can never blank a page or fail a render.
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Three rules a theme must keep: put the machine-readable form in the attribute and the localised form in the
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text — `<time datetime="{{.Date.Format "2006-01-02"}}">{{day .Lang .Date}}</time>`; never localise
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`.Title`, `.HTML` or anything else the author wrote; and never pass a URL, key or path segment through
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these functions. An address is not chrome (`content-model.md`).
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A site root cannot add or override a phrase yet. A theme needing its own words writes them in its own
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block; site-supplied strings wait for the settings cascade (`ideas/deferred-decisions.md`).
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## Shortcode fragments
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`templates/shortcodes.html` holds one named template per shortcode, and that is where a shortcode's markup
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lives — the engine parses the call and supplies its data, never any HTML (ADR-0036).
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Every fragment receives the same two fields (ADR-0037):
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| Field | Contents |
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| `.Args` | the call's `key="value"` pairs, exactly as the author wrote them |
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| `.Pictures` | images the *engine* gathered: one for a figure, many for a gallery, none when the call names nothing it recognises (ADR-0042) |
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Each picture carries:
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| Field | Contents |
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| `.Src` | the author's own file, relative to the bundle — always usable on its own |
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| `.Srcset` | the generated widths, closed by the original at its own width; empty when nothing was worth generating, or when the format has no decoder |
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| `.Width`, `.Height` | the original's intrinsic size, for reserving the box; zero when the file could not be read |
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| Shortcode | Template | Receives |
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| `{{< figure src="…" alt="…" caption="…" >}}` | `figure` | `.Args.src`, `.Args.alt`, `.Args.caption` |
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| `{{< gallery >}}` | `gallery` | `.Pictures` — every picture beside the bundle, in filename order |
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`{{< include file="…" >}}` has **no fragment**: an included file is content, so it renders as Markdown in
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place and a theme has nothing to style about it (ADR-0038).
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Authored and engine-supplied data are kept apart so a `src` argument can never be confused with a `src` the
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engine found. Arguments are escaped by `html/template` like any other data, in whichever context the
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template puts them — which is what keeps an author's text out of the markup. A call whose template is
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missing renders nothing and logs; it never fails the page.
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A gallery entry has no alt text: nothing in a filename supplies one, and inventing it would be worse than an
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empty `alt` on a picture the page has already introduced. A figure's alt is the author's, from `.Args.alt`.
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The set is overlaid the same way as the page kinds: a site's `templates/shortcodes.html` is parsed after
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the embedded one, so redefining `figure` replaces it and any fragment left alone is inherited. Argument
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names are contract, added but never renamed.
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## The stability rule
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Fields and names are **added, never renamed or removed**. Absence is always legal: a template reading a
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field that does not exist gets the zero value and must not crash, and the engine must not make a missing
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field fatal at request time (ADR-0002, invariant 1). This is the View-layer freeze from
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`architecture.md`, arriving as soon as a theme exists rather than at Arc 2.
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Breaking the contract is not a feature — it is a new contract version, and it needs an ADR.
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## What the engine provides
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| Provides | Detail |
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| the page object | known fields plus an `Extra` bag carrying unknown frontmatter (ADR-0002) |
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| the resolved cascade | settings after site → section → bundle resolution (`ideas/deferred-decisions.md`) |
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| queries the page needs | its sequence neighbours, its taxonomy terms, its section's members |
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| named template lookup | per-type sets; a theme redefines a named block and inherits the rest (ADR-0019) |
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| URLs | every path the engine emits, so a theme never constructs one by hand |
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| per-page assets | the `styles` / `scripts` frontmatter lists, resolved relative to the bundle |
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| chrome strings | looked up by key and language, never hardcoded English in a template — live, see above |
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| validity windows | a template that renders time-dependent output declares one |
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## Extras view
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For a request under a bundle's extras directory (`ideas/deferred-decisions.md`) the engine additionally provides:
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| Field | Contents |
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| `.Extras.Entries` | the tree: `Name`, `Path`, `URL`, `RawURL`, `Kind`, `Size`, `IsDir`, `ModTime` |
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| `.Extras.Selected` | nil on the bare listing; otherwise the chosen entry |
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| `.Extras.Selected.HTML` | rendered output for `markdown` and `text` kinds; empty otherwise |
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| `.Extras.Selected.RawURL` | always present — for `<img src>`, `<object data>`, or a download link |
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`.Bundle` is the parent, so a theme has its title, language and breadcrumb. Selecting an entry is an
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ordinary link and a full re-render, so a sidebar-plus-pane layout needs no JavaScript; swapping the pane
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client-side is a later enhancement over working markup, never a requirement.
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## What the engine does not provide
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Layout, class names, CSS, client-side behaviour, and any choice about how something *looks* — including
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how media is embedded, how a listing is arranged, and whether something appears in a sidebar. Those are
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theme decisions, and a request touching them is split: a contract extension here, a change there.
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The engine also does not provide a component library, a CSS build step, or a JavaScript runtime.
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`conventions.md` holds the output floor the engine itself meets — semantic HTML, zero-JS, every image
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carrying width, height and alt — and a theme is expected to stay inside it, but the engine does not
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enforce a theme's markup.
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## The reference theme
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The binary embeds a reference theme — templates plus one small stylesheet — so a bare site root renders
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(ADR-0026). It exists to make this document executable: it implements every field and block named here and
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nothing else, and a golden-file test through it catches contract regressions before a real theme does.
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It is not a design. Legibility only, no branding, no visual opinions, no JavaScript — `verify.sh` fails on
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a `<script` tag in it. If it starts accumulating taste, it has stopped being a reference.
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It demonstrates the contract; it is not the contract. Changing it does not change what a theme may rely on
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— which is why `verify.sh` also fails when it changes without this document changing, since in practice the
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two drift together.
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## Overriding it
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A site root's `templates/` is parsed **after** the embedded set, and the last definition of a name wins, so
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a theme redefines one named block and inherits the document (ADR-0019). Each set is built from named files
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and only those are overlaid — `base.html` plus that kind's block file (`page.html` or `list.html`), and
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`shortcodes.html` on its own. Overlaying every site template into every set would let a listing's `main`
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leak into bundle pages, which is the collision per-kind sets exist to prevent.
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`templates/theme.css` in the site root replaces the reference stylesheet entirely; there is no merging.
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`static/` in the site root is served verbatim under `/static/`. Directory paths answer 404 rather than
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listing their contents.
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## Splitting a request
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When a feature spans engine and theme, this repo delivers:
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1. the contract extension — new fields, new named blocks, new queries, new URLs;
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2. a note stating what a theme must do to use it, precise enough to act on without this conversation;
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3. embedded defaults updated far enough to prove the extension works.
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It does not deliver the theme. Claiming otherwise is the same error as claiming to have migrated content
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in a site root this repo cannot see.
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