RMT Reference: Surfaces, Lanes and Lifecycle

tools/rmt-language/vnext-surfaces.js and the scheduler emit the normalized runtime records.

Surfaces describe UI areas. Lanes schedule work. Lifecycle operations describe what happens in a lane.

Syntax

Operator	Form	Allowed contexts	Parameters	Function	Diagnostics	Related operators
`kind`	`surface shell kind page`	Surface header, overlay, resource	catalog value or identifier	Classifies a surface, overlay or resource.	Surface headers allow only `kind` and `component`.	`component`
`component`	`component x-section`	Surface header	custom element name or identifier	Binds a host component.	Unexpected header clauses are reported.	`surface`
`source`	`source selector app.items`	Surface, resource	source kind and reference	Binds a primitive record as source.	Missing references are semantic diagnostics.	`repeat from`
`repeat from`	`repeat from selector app.items`	Surface	source reference	Creates repeated surface instances.	Repeaters need stable keys.	`key`
`key`	`key item.id`	Surface	path	Declares the stable repeater key.	Unkeyed repeaters can be blocked.	`repeat from`
`bounds`	`bounds x 0 y 0 width 640 height 400`	Surface	key/value pairs	Sets initial geometry.	Bounds keys need values.	`surface`
`preserve on minimize`	`preserve on minimize`	Surface	raw clause	Preserves surface state when minimized.	Only valid in surface.	`preserve`
`destroy releases`	`destroy releases resource app.stream`	Surface	resource reference	Binds surface destroy to resource cleanup.	Resource must exist.	`resource`, `dispose`
`lane`	`lane visible weight 80 { ... }`	Surface	lane name, optional `weight`	Groups scheduled work.	Lanes may contain lifecycle or `stream` only.	`weight`, `mount`
`weight`	`weight 80`	Lane header	nonnegative integer	Prioritizes lane work.	Weight must be a nonnegative integer.	`lane`
`mount`	`mount card from endpoint app.card`	Lane, slot	target, optional source, condition, policy	Materializes new UI work.	Operations may not be top-level.	`slot`, `when`
`hydrate`	`hydrate card from selector app.card`	Lane, slot	target, source	Fills existing UI with data.	Source kind must be allowed.	`hydration policy`
`suspend`	`suspend card`	Lane, slot	target	Pauses a UI or resource unit.	Only valid in lane or slot.	`resume`
`resume`	`resume card`	Lane, slot	target	Resumes paused work.	Only valid in lane or slot.	`suspend`
`invalidate`	`invalidate card`	Lane, slot	target	Marks work for recomputation.	Only valid in lane or slot.	`update`
`dispose`	`dispose card`	Lane, slot, resource block	target or cleanup text	Releases work or a resource.	Wrong context is reported.	`destroy releases`
`prewarm`	`prewarm data from worker prepare`	Lane, slot	target, source	Prepares data or UI before it becomes visible.	Source kind must be static.	`worker`, `idle`
`recycle`	`recycle row from resource pool`	Lane, slot	target, source	Reuses existing instances.	Resource must exist.	`resource`
`detach`	`detach panel`	Lane, slot	target	Detaches a surface unit from the current host context.	Only valid in lane or slot.	`reattach`
`reattach`	`reattach panel`	Lane, slot	target	Attaches a detached unit again.	Only valid in lane or slot.	`detach`
`stream`	`stream feed from sse app.feed`	Lane, slot	target, source	Describes incremental rendering data.	`stream` requires a data source.	`sse`, `sanitize`
`slot`	`slot header { hydrate title from selector app.title }`	Policy block	slot name	Groups operations in a composition slot.	Slots allow only lifecycle or `stream`.	`mount`, `hydrate`
`resumability`	`resumability mode server_prerender_resume`	Policy block	`mode`, `snapshot`, `event replay` or `integrity`	Declares full SSR resumability as a resume handoff.	Clauses must be static and use a known resumability axis.	`hydration mode`, `resume`

Allowed contexts

lane belongs directly in surface. Lifecycle operations and stream belong in lane or slot. slot, on, trust, hydration, resumability, isolation and sanitize belong in lifecycle policy blocks.

bounds stays pixel-exact by default; responsive bounds are opt-in and accept quoted CSS-native sizes, for example bounds mode responsive scope viewport x "1rem" y "1rem" width "clamp(20rem, 70vi, 52rem)" height "min(80dvh, 42rem)" minWidth "18rem" maxHeight "48rem".

Parameters

Targets are identifiers. Sources follow from <kind> <target>. Conditions follow when. Policy blocks use braces.

Description

Lifecycle syntax separates visible work, user-blocking interaction, background work and diagnostics. The host can map these records to scheduler lanes without executing free functions from the RMT source.

Examples

template reference.lifecycle {
  state app.ready type boolean initial true
  state app.status type object preserve {
    initial {
      text "Ready"
    }
  }
  selector app.header from state app.status {
    output HeaderView
  }
  selector app.cardView from state app.status {
    output CardView
  }
  resource app.stream kind stream owner surface.shell
  resource app.pool kind object-url owner surface.shell
  portal app.root root "#app" layer surface

  surface shell kind page component x-section {
    portal app.root
    bounds x 0 y 0 width 640 height 400
    preserve on minimize
    destroy releases resource app.stream
    lane visible weight 90 {
      mount shell.card from endpoint app.card when app.ready == true {
        slot header {
          hydrate header.view from selector app.header
        }
        on click ".save" -> action app.save {
          payload id from target.dataset.id
          preventDefault true
        }
      }
      hydrate shell.card from selector app.cardView {
        hydration mode server_prerender_resume
        resumability mode server_prerender_resume
        resumability snapshot surface_state
        resumability event replay intent_queue
        resumability integrity signed_manifest
      }
      suspend shell.card
      resume shell.card {
        resumability mode server_prerender_resume
        resumability snapshot surface_state
        resumability event replay intent_queue
        resumability integrity signed_manifest
      }
      invalidate shell.card
      dispose shell.card
      prewarm shell.data from worker app.prepare
      recycle shell.row from resource app.pool
      detach shell.panel
      reattach shell.panel
      stream shell.feed from sse app.feed
    }
  }

  action app.save {
    input id string
    reduce state.app.status.text = "Saved"
    emit app.saved with id input.id
  }
}

Diagnostics

Lifecycle and stream statements outside lanes or slots produce context diagnostics. Missing selector, resource or action references are reported semantically.

surface, portal, source, when, slot, on, resource, trust boundary.

The RMT reference index connects surfaces and lanes with scheduling and lifecycle syntax. Related article

XTend Developer Center