forked from lix-project/lix
276 lines
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Markdown
276 lines
10 KiB
Markdown
# Glossary
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- [derivation]{#gloss-derivation}
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A description of a build task. The result of a derivation is a
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store object. Derivations are typically specified in Nix expressions
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using the [`derivation` primitive](./language/derivations.md). These are
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translated into low-level *store derivations* (implicitly by
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`nix-env` and `nix-build`, or explicitly by `nix-instantiate`).
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[derivation]: #gloss-derivation
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- [store derivation]{#gloss-store-derivation}
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A [derivation] represented as a `.drv` file in the [store].
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It has a [store path], like any [store object].
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Example: `/nix/store/g946hcz4c8mdvq2g8vxx42z51qb71rvp-git-2.38.1.drv`
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See [`nix derivation show`](./command-ref/new-cli/nix3-derivation-show.md) (experimental) for displaying the contents of store derivations.
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[store derivation]: #gloss-store-derivation
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- [instantiate]{#gloss-instantiate}, instantiation
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Translate a [derivation] into a [store derivation].
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See [`nix-instantiate`](./command-ref/nix-instantiate.md).
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[instantiate]: #gloss-instantiate
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- [realise]{#gloss-realise}, realisation
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Ensure a [store path] is [valid][validity].
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This means either running the [`builder`](@docroot@/language/derivations.md#attr-builder) executable as specified in the corresponding [derivation], or fetching a pre-built [store object] from a [substituter], or delegating to a [remote builder](@docroot@/advanced-topics/distributed-builds.html) and retrieving the outputs. <!-- TODO: link [running] to build process page, #8888 -->
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See [`nix-build`](./command-ref/nix-build.md) and [`nix-store --realise`](@docroot@/command-ref/nix-store/realise.md).
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See [`nix build`](./command-ref/new-cli/nix3-build.md) (experimental).
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[realise]: #gloss-realise
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- [content-addressed derivation]{#gloss-content-addressed-derivation}
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A derivation which has the
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[`__contentAddressed`](./language/advanced-attributes.md#adv-attr-__contentAddressed)
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attribute set to `true`.
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- [fixed-output derivation]{#gloss-fixed-output-derivation}
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A derivation which includes the
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[`outputHash`](./language/advanced-attributes.md#adv-attr-outputHash) attribute.
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- [store]{#gloss-store}
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The location in the file system where store objects live. Typically
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`/nix/store`.
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From the perspective of the location where Nix is
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invoked, the Nix store can be referred to
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as a "_local_" or a "_remote_" one:
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+ A [local store]{#gloss-local-store} exists on the filesystem of
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the machine where Nix is invoked. You can use other
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local stores by passing the `--store` flag to the
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`nix` command. Local stores can be used for building derivations.
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+ A *remote store* exists anywhere other than the
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local filesystem. One example is the `/nix/store`
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directory on another machine, accessed via `ssh` or
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served by the `nix-serve` Perl script.
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[store]: #gloss-store
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[local store]: #gloss-local-store
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- [chroot store]{#gloss-chroot-store}
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A [local store] whose canonical path is anything other than `/nix/store`.
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- [binary cache]{#gloss-binary-cache}
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A *binary cache* is a Nix store which uses a different format: its
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metadata and signatures are kept in `.narinfo` files rather than in a
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[Nix database]. This different format simplifies serving store objects
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over the network, but cannot host builds. Examples of binary caches
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include S3 buckets and the [NixOS binary cache](https://cache.nixos.org).
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- [store path]{#gloss-store-path}
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The location of a [store object] in the file system, i.e., an
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immediate child of the Nix store directory.
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Example: `/nix/store/a040m110amc4h71lds2jmr8qrkj2jhxd-git-2.38.1`
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[store path]: #gloss-store-path
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- [file system object]{#gloss-store-object}
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The Nix data model for representing simplified file system data.
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See [File System Object](@docroot@/architecture/file-system-object.md) for details.
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[file system object]: #gloss-file-system-object
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- [store object]{#gloss-store-object}
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A store object consists of a [file system object], [reference]s to other store objects, and other metadata.
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It can be referred to by a [store path].
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[store object]: #gloss-store-object
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- [input-addressed store object]{#gloss-input-addressed-store-object}
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A store object produced by building a
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non-[content-addressed](#gloss-content-addressed-derivation),
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non-[fixed-output](#gloss-fixed-output-derivation)
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derivation.
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- [output-addressed store object]{#gloss-output-addressed-store-object}
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A [store object] whose [store path] is determined by its contents.
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This includes derivations, the outputs of [content-addressed derivations](#gloss-content-addressed-derivation), and the outputs of [fixed-output derivations](#gloss-fixed-output-derivation).
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- [substitute]{#gloss-substitute}
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A substitute is a command invocation stored in the [Nix database] that
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describes how to build a store object, bypassing the normal build
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mechanism (i.e., derivations). Typically, the substitute builds the
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store object by downloading a pre-built version of the store object
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from some server.
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- [substituter]{#gloss-substituter}
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An additional [store]{#gloss-store} from which Nix can obtain store objects instead of building them.
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Often the substituter is a [binary cache](#gloss-binary-cache), but any store can serve as substituter.
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See the [`substituters` configuration option](./command-ref/conf-file.md#conf-substituters) for details.
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[substituter]: #gloss-substituter
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- [purity]{#gloss-purity}
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The assumption that equal Nix derivations when run always produce
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the same output. This cannot be guaranteed in general (e.g., a
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builder can rely on external inputs such as the network or the
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system time) but the Nix model assumes it.
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- [Nix database]{#gloss-nix-database}
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An SQlite database to track [reference]s between [store object]s.
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This is an implementation detail of the [local store].
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Default location: `/nix/var/nix/db`.
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[Nix database]: #gloss-nix-database
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- [Nix expression]{#gloss-nix-expression}
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A high-level description of software packages and compositions
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thereof. Deploying software using Nix entails writing Nix
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expressions for your packages. Nix expressions are translated to
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derivations that are stored in the Nix store. These derivations can
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then be built.
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- [reference]{#gloss-reference}
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A [store object] `O` is said to have a *reference* to a store object `P` if a [store path] to `P` appears in the contents of `O`.
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Store objects can refer to both other store objects and themselves.
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References from a store object to itself are called *self-references*.
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References other than a self-reference must not form a cycle.
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[reference]: #gloss-reference
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- [reachable]{#gloss-reachable}
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A store path `Q` is reachable from another store path `P` if `Q`
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is in the *closure* of the *references* relation.
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- [closure]{#gloss-closure}
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The closure of a store path is the set of store paths that are
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directly or indirectly “reachable” from that store path; that is,
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it’s the closure of the path under the *references* relation. For
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a package, the closure of its derivation is equivalent to the
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build-time dependencies, while the closure of its output path is
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equivalent to its runtime dependencies. For correct deployment it
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is necessary to deploy whole closures, since otherwise at runtime
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files could be missing. The command `nix-store --query --requisites ` prints out
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closures of store paths.
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As an example, if the [store object] at path `P` contains a [reference]
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to a store object at path `Q`, then `Q` is in the closure of `P`. Further, if `Q`
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references `R` then `R` is also in the closure of `P`.
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[closure]: #gloss-closure
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- [output]{#gloss-output}
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A [store object] produced by a [derivation].
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[output]: #gloss-output
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- [output path]{#gloss-output-path}
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The [store path] to the [output] of a [derivation].
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[output path]: #gloss-output-path
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- [deriver]{#gloss-deriver}
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The [store derivation] that produced an [output path].
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- [validity]{#gloss-validity}
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A store path is valid if all [store object]s in its [closure] can be read from the [store].
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For a [local store], this means:
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- The store path leads to an existing [store object] in that [store].
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- The store path is listed in the [Nix database] as being valid.
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- All paths in the store path's [closure] are valid.
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[validity]: #gloss-validity
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- [user environment]{#gloss-user-env}
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An automatically generated store object that consists of a set of
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symlinks to “active” applications, i.e., other store paths. These
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are generated automatically by
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[`nix-env`](./command-ref/nix-env.md). See *profiles*.
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- [profile]{#gloss-profile}
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A symlink to the current *user environment* of a user, e.g.,
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`/nix/var/nix/profiles/default`.
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- [installable]{#gloss-installable}
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Something that can be realised in the Nix store.
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See [installables](./command-ref/new-cli/nix.md#installables) for [`nix` commands](./command-ref/new-cli/nix.md) (experimental) for details.
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- [NAR]{#gloss-nar}
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A *N*ix *AR*chive. This is a serialisation of a path in the Nix
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store. It can contain regular files, directories and symbolic
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links. NARs are generated and unpacked using `nix-store --dump`
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and `nix-store --restore`.
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- [`∅`]{#gloss-emtpy-set}
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The empty set symbol. In the context of profile history, this denotes a package is not present in a particular version of the profile.
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- [`ε`]{#gloss-epsilon}
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The epsilon symbol. In the context of a package, this means the version is empty. More precisely, the derivation does not have a version attribute.
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- [string interpolation]{#gloss-string-interpolation}
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Expanding expressions enclosed in `${ }` within a [string], [path], or [attribute name].
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See [String interpolation](./language/string-interpolation.md) for details.
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[string]: ./language/values.md#type-string
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[path]: ./language/values.md#type-path
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[attribute name]: ./language/values.md#attribute-set
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- [experimental feature]{#gloss-experimental-feature}
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Not yet stabilized functionality guarded by named experimental feature flags.
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These flags are enabled or disabled with the [`experimental-features`](./command-ref/conf-file.html#conf-experimental-features) setting.
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See the contribution guide on the [purpose and lifecycle of experimental feaures](@docroot@/contributing/experimental-features.md).
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