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    #@transform

    A composable DOM rewrite pipeline. Build an array of TransformSpec values and hand them to apply_transforms along with a node. Each spec runs over the tree in order and can drop, unwrap, escape, edit, or annotate matching elements.

    The examples below are mbt check blocks and run as part of moon test transform.

    #The five element actions

    ///|
    pub(all) enum DecideAction {
      Keep // leave alone
      Drop // remove the element and its subtree
      Unwrap // remove the tag but splice children up
      Empty // keep the tag, remove the children
      Escape // serialize the tag to its HTML-escaped text form
    }

    Each action has a dedicated constructor (drop, unwrap, escape, empty) and decide runs your callback to pick per node.

    ///|
    test "readme transform actions" {
      let frag = @dom.fragment(children=[
        @dom.element("script", children=[@dom.text("alert(1)")]),
        @dom.element("font", children=[@dom.text("loud")]),
      ])
      let out = @transform.apply_transforms(frag, [
        @transform.TransformSpec::drop("script"),
        @transform.TransformSpec::unwrap("font"),
      ])
      inspect(
        @ser.to_html(out, pretty=false),
        content=(
          #|loud
        ),
      )
    }

    #Shaping attributes

    drop_attrs, set_attrs, allowlist_attrs, merge_attrs, and edit_attrs cover the common attribute changes. merge_attrs is especially handy for token-list attributes like rel:

    ///|
    test "readme transform merge_attrs" {
      let frag = @dom.fragment(children=[
        @dom.element(
          "a",
          attrs={ "href": Some("https://example.com"), "rel": Some("nofollow") },
          children=[@dom.text("link")],
        ),
      ])
      let out = @transform.apply_transforms(frag, [
        @transform.TransformSpec::merge_attrs("a", attr="rel", tokens=[
          "noopener", "noreferrer",
        ]),
      ])
      inspect(
        @ser.to_html(out, pretty=false),
        content=(
          #|<a href="https://example.com" rel="nofollow noopener noreferrer">link</a>
        ),
      )
    }

    #Composing with stage

    stage bundles a set of transforms into one logical spec — useful when you want to keep your top-level pipeline short.

    ///|
    test "readme transform stage" {
      let frag = @dom.fragment(children=[
        @dom.element("script", children=[@dom.text("evil")]),
        @dom.comment(" tracking "),
        @dom.element("p", children=[@dom.text("keep")]),
      ])
      let cleanup = @transform.TransformSpec::stage([
        @transform.TransformSpec::drop("script"),
        @transform.TransformSpec::drop_comments(),
      ])
      let out = @transform.apply_transforms(frag, [cleanup])
      inspect(
        @ser.to_html(out, pretty=false),
        content=(
          #|<p>keep</p>
        ),
      )
    }

    #Feature-flagging with enabled

    Every spec constructor accepts enabled=false to skip the step without restructuring the pipeline.

    ///|
    test "readme transform enabled flag" {
      let frag = @dom.fragment(children=[
        @dom.element("script", children=[@dom.text("kept")]),
      ])
      let out = @transform.apply_transforms(frag, [
        @transform.TransformSpec::drop("script", enabled=false),
      ])
      inspect(
        @ser.to_html(out, pretty=false),
        content=(
          #|<script>kept</script>
        ),
      )
    }

    #Telemetry hooks

    Every spec constructor also accepts hook= (called per matching node) and report= (called with a string code and optional node when the spec changes something). They let you collect counters and audit trails without altering the rewrite itself.

    DecideAction

    source
    pub(all) enum DecideAction {
      Keep
      Drop
      Unwrap
      Empty
      Escape
    } derive(Eq, 
    Debug    )

    Action returned by a TransformSpec::decide callback.

    Keep leaves the matched node unchanged. The other variants apply the same structural operations as the corresponding selector transforms.

    DecideAction::equal

    source
    #deprecated("implicit derived-impl promotion; call the trait method directly")
    fn DecideAction::equal(DecideAction, DecideAction) -> Bool

    DecideAction::not_equal

    source
    #deprecated("implicit derived-impl promotion; call the trait method directly")
    fn DecideAction::not_equal(x : DecideAction, y : DecideAction) -> Bool

    DecideAction::to_repr

    source
    #deprecated("implicit derived-impl promotion; call the trait method directly")
    fn DecideAction::to_repr(DecideAction) -> 
    Repr

    TransformSpec

    source
    pub struct TransformSpec {
      // private fields
    } derive(
    Debug    )

    A DOM transform specification for apply_transforms.

    The current port covers deterministic structural, attribute, callback, URL/style, utility, and sanitizer transforms. Most selector and node-kind transforms also support hook/report callbacks.

    TransformSpec::allow_style_attrs

    source
    fn TransformSpec::allow_style_attrs(selector : StringView, allowed_css_properties~ : Array[String], enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that sanitizes inline style attributes.

    TransformSpec::allowlist_attrs

    source
    fn TransformSpec::allowlist_attrs(selector : StringView, allowed_attributes : Map[String, Array[String]], enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that keeps only allowed attributes on matching elements.

    TransformSpec::collapse_whitespace

    source
    fn TransformSpec::collapse_whitespace(skip_tags? : Array[String], enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that collapses runs of HTML whitespace in text nodes.

    TransformSpec::decide

    source
    fn TransformSpec::decide(selector : StringView, callback : (
    Node    ) -> DecideAction, enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that chooses a structural action for matching nodes.

    TransformSpec::drop

    source
    fn TransformSpec::drop(selector : StringView, enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that removes elements matching selector.

    TransformSpec::drop_attrs

    source
    fn TransformSpec::drop_attrs(selector : StringView, patterns : Array[String], enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that removes matching attributes from matching elements.

    TransformSpec::drop_comments

    source
    fn TransformSpec::drop_comments(enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that removes comment nodes.

    TransformSpec::drop_doctype

    source
    fn TransformSpec::drop_doctype(enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that removes doctype nodes.

    TransformSpec::drop_foreign_namespaces

    source
    fn TransformSpec::drop_foreign_namespaces(enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that removes elements outside the HTML namespace.

    TransformSpec::drop_url_attrs

    source
    fn TransformSpec::drop_url_attrs(selector : StringView, url_policy~ : 
    UrlPolicy    , enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that validates URL-valued attributes with url_policy.

    TransformSpec::edit

    source
    fn TransformSpec::edit(selector : StringView, callback : (
    Node    ) -> Unit, enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that invokes callback for matching elements.

    TransformSpec::edit_attrs

    source
    fn TransformSpec::edit_attrs(selector : StringView, callback : (
    Node    ) -> Map[String, String?]?, enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that replaces matching element attributes when callback returns a map.

    TransformSpec::edit_document

    source
    fn TransformSpec::edit_document(callback : (
    Node    ) -> Unit, enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that invokes callback once on the supplied root.

    TransformSpec::empty

    source
    fn TransformSpec::empty(selector : StringView, enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that removes all children from matching elements.

    TransformSpec::escape

    source
    fn TransformSpec::escape(selector : StringView, enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that emits matching element tags as text and keeps children.

    TransformSpec::linkify

    source
    fn TransformSpec::linkify(config? : 
    LinkifyConfig    , skip_tags? : Array[String], enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that linkifies URL and email text nodes.

    TransformSpec::merge_attrs

    source
    fn TransformSpec::merge_attrs(tag : StringView, attr~ : StringView, tokens~ : Array[String], enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that merges tokens into a whitespace-delimited attribute.

    TransformSpec::prune_empty

    source
    fn TransformSpec::prune_empty(selector : StringView, strip_whitespace? : Bool, enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that recursively removes empty matching elements.

    TransformSpec::sanitize

    source

    Build a transform that sanitizes the DOM tree with an optional policy.

    TransformSpec::set_attrs

    source
    fn TransformSpec::set_attrs(selector : StringView, attrs : Map[String, String?], enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that sets or adds attributes on matching elements.

    TransformSpec::stage

    source
    fn TransformSpec::stage(transforms : Array[TransformSpec], enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build an explicit transform stage. Stages split a transform list into separate passes and may report against the current root before the pass.

    TransformSpec::to_repr

    source

    TransformSpec::unwrap

    source
    fn TransformSpec::unwrap(selector : StringView, enabled? : Bool, hook? : (
    Node    ) -> Unit, report? : (String, 
    Node    ?) -> Unit) -> TransformSpec

    Build a transform that replaces matching elements with their children.

    apply_transforms

    source

    Apply DOM transforms in order.

    The transform mutates and returns the current root. Selector transforms process the children of the supplied root, matching the Python constructor-time pipeline where the root is normally a document or document fragment container.

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