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+## Expression, Markup, and Message Attributes
+
+> [!IMPORTANT]
+> This part of the specification is under incubation by the MessageFormat WG,
+> and may end up being finalized elsewhere.
+> It is non-normative.
+
+### Expression and Markup Attributes
+
+- [@can-copy](expression-and-markup.md#can-copy)
+- [@can-delete](expression-and-markup.md#can-delete)
+- [@can-overlap](expression-and-markup.md#can-overlap) (Markup only)
+- [@can-reorder](expression-and-markup.md#can-reorder) (Markup only)
+- [@comment](expression-and-markup.md#comment)
+- [@example](expression-and-markup.md#example) (Expression only)
+- [@term](expression-and-markup.md#term)
+- [@translate](mexpression-and-markup.md#translate)
+
+### Message Attributes
+
+- [@allow-empty](message.md#allow-empty)
+- [@obsolete](message.md#obsolete)
+- [@param](message.md#param)
+- [@schema](message.md#schema)
+- [@translate](message.md#translate)
+
+### Attribute Values
+
+_Attributes_ are not required to have a value.
+For _attributes_ defined here that explicitly support `yes` as a value,
+an _attribute_ with no value is considered synonymous
+with the same _attribute_ with the value `yes`.
diff --git a/spec/attributes/expression-and-markup.md b/spec/attributes/expression-and-markup.md
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+## Expression and Markup Attributes
+
+> [!IMPORTANT]
+> This part of the specification is under incubation by the MessageFormat WG,
+> and may end up being finalized elsewhere.
+> It is non-normative.
+
+The Unicode MessageFormat syntax and data model allow for _attributes_
+to be defined on _expressions_ and _markup_.
+These MUST NOT have any impact on the _formatting_ of a message,
+and are intended to inform users, such as translators, and tools
+about the specific _expressions_ or _markup_ to which they are attached.
+_Attributes_ MAY be stripped from _expressions_ and _markup_
+with no effect on the message's _formatting_.
+
+As all _attributes_ with _reserved identifiers_ are reserved,
+definitions are provided here for common _attribute_ use cases.
+Use a _custom identifier_ for other (custom) _attributes_,
+preferably one with an appropriate _namespace_.
+
+### @can-copy
+
+_Value:_ `yes` or `no`.
+
+Indicates whether or not the _expression_ or the _markup_ and its contents can be copied.
+
+This corresponds to
+the [XLIFF 2 `canCopy` attribute](https://docs.oasis-open.org/xliff/xliff-core/v2.2/xliff-core-v2.2-part1.html#cancopy).
+
+> For example:
+>
+> ```
+> Have a {#span @can-copy}great and wonderful{/span @can-copy} birthday!
+> ```
+
+### @can-delete
+
+_Value:_ `yes` or `no`.
+
+Indicates whether or not the _expression_ or the _markup_ and its contents can be deleted.
+
+This corresponds to
+the [XLIFF 2 `canDelete` attribute](https://docs.oasis-open.org/xliff/xliff-core/v2.2/xliff-core-v2.2-part1.html#candelete).
+
+### @can-overlap (Markup only)
+
+_Value:_ `yes` or `no`.
+
+Indicates whether or not the _markup_ and its contents where this _attribute_ is used
+can enclose partial _markup_
+(i.e. a _markup-open_ without its corresponding _markup-end_,
+or a _markup-end_ without its corresponding _markup-start_).
+
+This corresponds to
+the [XLIFF 2 `canOverlap` attribute](https://docs.oasis-open.org/xliff/xliff-core/v2.2/xliff-core-v2.2-part1.html#canoverlap).
+
+### @can-reorder (Markup only)
+
+_Value:_ `yes` or `no`.
+
+Indicates whether or not the _markup_ and its contents can be re-ordered.
+
+This corresponds to
+the [XLIFF 2 `canReorder` attribute](https://docs.oasis-open.org/xliff/xliff-core/v2.2/xliff-core-v2.2-part1.html#canreorder).
+
+### @comment
+
+_Value_: A non-empty string.
+
+Associates a freeform comment with an _expression_ or _markup_.
+
+This corresponds to
+the [ITS 2 Localization Note data category](https://www.w3.org/TR/its20/#locNote-datacat), and
+the [XLIFF 2 comment annotation](https://docs.oasis-open.org/xliff/xliff-core/v2.2/xliff-core-v2.2-part1.html#commentAnnotation).
+
+> For example:
+>
+> ```
+> The {$device @comment=|Possible values: Printer or Stacker|} has been enabled.
+> ```
+>
+> ```
+> Click {#link @comment=|Rendered as a button|}here{/link} to continue.
+> ```
+
+### @example (Expression only)
+
+_Value_: A non-empty string.
+
+An example of the value the _expression_ might take.
+
+> For example:
+>
+> ```
+> Error: {$details @example=|Failed to fetch RSS feed.|}
+> ```
+
+### @term
+
+_Value_: A non-empty string, or a URI.
+
+Identifies a well-defined term.
+The value may be a short definition of the term,
+or a URI pointing to such a definition.
+
+This corresponds to
+the [ITS 2 Terminology data category](https://www.w3.org/TR/its20/#terminology), and
+the [XLIFF 2 term annotation](https://docs.oasis-open.org/xliff/xliff-core/v2.2/xliff-core-v2.2-part1.html#termAnnotation).
+
+> For example:
+>
+> ```
+> He saw his {|doppelgänger| @term=|https://en.wikipedia.org/wiki/Doppelg%C3%A4nger|}.
+> ```
+>
+> ```
+> He saw his {#span @term=|https://en.wikipedia.org/wiki/Doppelg%C3%A4nger|}doppelgänger{/span}.
+> ```
+
+### @translate
+
+_Value:_ `yes` or `no`.
+
+Indicates whether the _expression_ or the _markup_ and its contents are translatable or not.
+
+This corresponds to
+the [HTML `translate` attribute](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Global_attributes/translate),
+the [ITS 2 Translate data category](https://www.w3.org/TR/its20/#trans-datacat), and
+the [XLIFF 2 translate annotation](https://docs.oasis-open.org/xliff/xliff-core/v2.2/xliff-core-v2.2-part1.html#translateAnnotation).
+
+> For example:
+>
+> ```
+> He saw his {|doppelgänger| @translate=no}.
+> ```
+>
+> ```
+> He saw his {#span @translate=no}doppelgänger{/span}.
+> ```
diff --git a/spec/attributes/message.md b/spec/attributes/message.md
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+## Message Attributes
+
+> [!IMPORTANT]
+> This part of the specification is under incubation by the MessageFormat WG,
+> and may end up being finalized elsewhere.
+> It is non-normative.
+
+This specification does not define a means of attaching an _attribute_
+to the _message_ as a whole.
+In general, resource formats and containers of
+Unicode MessageFormat _messages_ provide their own such mechanisms.
+
+At least for now, the syntax of message attributes is
+outside the scope of this specification.
+
+### @allow-empty
+
+_Value:_ `yes` or `no`.
+
+Explicitly mark a message with an empty _pattern_ as valid.
+
+Most empty messages are mistakes,
+so being able to mark ones that can be empty is useful.
+
+Empty _messages_ SHOULD be accompanied by an explanatory `@comment`.
+
+### @obsolete
+
+_Value:_ `yes` or `no`.
+
+Explicitly mark a _message_ as obsolete.
+
+This might be used in workflows where messages are not immediately removed
+when they are no longer referenced by code,
+but kept in to support patch releases for previous versions.
+During translation, this can be used to de-prioritize such messages.
+
+> [!NOTE]
+> The value could include a way to note some version or timestamp when the removal happened,
+> or be paired with a second `@removed-in` or similar tag.
+
+### @param
+
+_Value_: **TBD**
+
+Documents a _variable_.
+
+> [!NOTE]
+> Having a well-defined structure for this attribute is pretty important,
+> at least to identify the variable its description is pertaining to.
+> In addition to describing the variable in words, it could include:
+> - The variable's type -- is it a string, a number, something else?
+> - A default example value to use for the variable.
+
+### @schema
+
+_Value:_ A valid URI.
+
+Identify the _functions_ and _markup_ supported by the _message_ formatter.
+
+### @translate
+
+_Value:_ `yes` or `no`
+
+Indicates whether the _message_ is translatable or not.
+
+Some _messages_ may be required to have the same value in all locales.