# Capability matrix Version 1 describes Fluffy's initial public compatibility surface. The table uses the two backends selected at session startup. The Phoenix backend chooses the Static or LiveView driver for every page; the Playwright backend uses the Playwright driver. The matrix records which backend provides each feature and where its drivers have explicit boundaries. A status applies only to the feature as described here and in its conformance tests; it is not a claim that an Elixir DOM is a complete browser implementation. - **equivalent** — the paired oracle corpus demonstrates the supported public contract; - **structural subset** — Phoenix implements DOM-represented facts and names the excluded browser facts; - **-** — this backend does not provide the behavior; - **experimental** — no stable initial-release contract is advertised. `-` covers both features that require a browser and features that do not apply to that backend. | Feature | Phoenix | Playwright | | --- | --- | --- | | Documented CSS locator subset | equivalent | equivalent | | Text, label, and attribute locators | equivalent | equivalent | | Structural role and accessible-name subset | structural subset | equivalent | | DOM assertions and strictness | equivalent | equivalent | | Page title assertions | equivalent | equivalent | | Indeterminate checkbox/radio DOM property | - | equivalent | | Structural element actions | structural subset | equivalent | | Visits, reloads, links, redirects, cookies, and HTTP forms | equivalent | equivalent | | Phoenix.HTML data-method/data-to actions | structural subset | equivalent | | LiveView events, patches, navigation, and structural action retry | equivalent | equivalent | | LiveView form-change delivery and timing | structural subset | equivalent | | Declarative LiveView keyboard events | structural subset | equivalent | | Supported mutable form state and ordered submission | equivalent | equivalent | | Structural Enter implicit form submission | structural subset | equivalent | | Native constraint validation | - | equivalent | | Specialized scalar input values | structural subset | equivalent | | Computed style, layout, and browser accessibility tree | - | equivalent | | Downloads | equivalent | equivalent | | Named pages and new tabs | - | equivalent | | Dialogs and browser request/response events | - | equivalent | | Active-page JavaScript evaluation | - | equivalent | | JavaScript-owned DOM and default actions | - | equivalent | | Native invalid, submit, and formdata event ordering | - | equivalent | | Hard-wrapped textarea, object, and custom-element entries | - | equivalent | | Per-test sessions, cleanup, and Ecto sandbox propagation | equivalent | equivalent | | Regex URL matching | equivalent | equivalent | | Structured path, query, and fragment URL matching | equivalent | equivalent | | Typed file selection and supported upload lifecycle | equivalent | equivalent | | Script-opened file chooser events | - | equivalent | ## Boundaries ### When to choose Playwright The Phoenix backend operates on parsed HTML plus Fluffy-owned mutable properties. Its drivers deliberately ignore layout, generated content, and computed visibility rather than attempting partial CSS analysis; use Playwright when a test asserts those facts. Native-validation behavior, arbitrary JavaScript, browser network streams, and JavaScript-created events are Playwright territory too. The matrix uses `-` for those boundaries rather than pretending that server-rendered HTML can bark like a browser. ### LiveView timing and keyboard events LiveView eagerly dispatches each applicable form-control `phx-change` and ignores `phx-debounce`/`phx-throttle` scheduling. Use Playwright for delay, blur-only delivery, coalescing, cancellation, and throttle suppression. For Enter, Space, and Tab, LiveView dispatches the supported direct and window `phx-keydown`/`phx-keyup` bindings, filters `phx-key`, preserves `phx-target`, and orders events around the structural default action. Application-defined LiveSocket metadata, modifiers and chords, repeats, browser timing, inline listeners, and client-side `JS` commands remain Playwright-only. ### LiveView document and patch boundaries On a LiveView page, the in-process locator and action surface is limited to the DOM owned by the current `Phoenix.LiveViewTest.View`. The dead layout surrounding `[data-phx-main]` is part of the browser document but not the LiveViewTest event tree, so Fluffy does not merge it into the in-process LiveView DOM. Initial outer-layout rendering assertions remain direct `Phoenix.ConnTest` response coverage; interactions with that layout use Playwright. This prevents a locator from resolving an element that the selected in-process driver cannot act upon. LiveView `unwrap/2` exposes only the View and therefore does not bypass this boundary. ### Browser baseline The stable compatibility baseline is pinned Chromium. Firefox and WebKit support is inherited from Playwright rather than verified by a duplicate Fluffy engine matrix. Known platform differences remain tagged in the conformance corpus so applications selecting another engine have explicit boundaries without weakening the shared Chromium contract. ### Phoenix.HTML actions and dialogs For a Static or LiveView target with `data-confirm`, `click/2` ignores the attribute and continues with the normal structural action. It does not create, inspect, accept, or dismiss a browser dialog; use Playwright whenever the prompt or its cancellation path is part of the assertion. Both in-process drivers model the pinned Phoenix.HTML `data-method`/`data-to` hidden-form action for plain elements, including links and buttons. Custom `phoenix.link.click` listeners, cancellation, and competing LiveView actions remain browser-only. ### Forms and files An `equivalent` form claim applies to the supported form model, not general native constraint validation. Static and LiveView bypass native validation and submit structurally; only Playwright models invalid events and blocking. The claim also excludes browser sanitization/defaults for specialized scalar input states and custom/form-associated elements. Static does reproduce multipart text entries and browser-shaped empty-file entries when no file has been selected. The file-selection row covers bounded local paths and typed in-memory payloads, ordered multiple selection, clearing, ordinary multipart forms, and the paired managed-LiveView validation, progress, cancellation, replacement, auto-upload, and submission lifecycle. Native picker UI, external uploaders, directories, drag-and-drop, and arbitrary `FileList` mutation remain outside that contract. `Event.file_chooser/2` is separately Playwright-only because it depends on application JavaScript opening a browser chooser. Static and LiveView retain specialized scalar input values as supplied strings; Playwright remains the browser-semantics oracle. ### URL matching `Page.to_have_url/1` runs one matcher against the canonical serialized page URL for Static, LiveView, and Playwright. Exact strings include query serialization and fragment; relative strings resolve against the session base URL. Elixir regular expressions see the same complete string on every driver. The structured form can select `:path`, `:query`, and `:fragment`. Omitted components are ignored. Query matching decodes names and values with URLSearchParams semantics, ignores distinct-name order, and retains repeated value order and duplicates. Exact mode rejects unrelated names; subset mode allows them while requiring the complete ordered values for every requested name. ### Native escape hatch `Fluffy.unwrap/2` is deliberately absent from the equivalence rows. It is one public entry point to three driver-native APIs, not a portable behavior: Static receives a `Plug.Conn`, LiveView receives a LiveViewTest `View`, and Playwright receives a `Fluffy.Playwright.Handle`. Conformance checks only the resulting state through ordinary shared assertions. Lifecycle and listener-before-action behaviors remain owned by the named Fluffy APIs.