Schemas / v0.4

Components

Definitions-only, composable lifecycle fragments for Custom Elements Manifest entries. This document is not a validator for a full Custom Elements Manifest; consumers apply the relevant definition alongside their pinned CEM schema.

This is not the Custom Elements Manifest (CEM) schema itself, and it defines no manifest of its own — the fragment has no root scope to validate. It defines extension fields that a design system may add to CEM entries — declarations, attributes, members, slots, cssProperties, cssParts, and events — to record lifecycle metadata: status, deprecation details, and migration targets. Consumers apply the relevant definition alongside their pinned CEM schema.

Applying the extensions

The snippet below is a Custom Elements Manifest declaration with the extension fields applied: status and deprecated on the declaration, and a deprecated attribute value with its migration path. The fragment does not validate the surrounding CEM document, so this example is illustrative rather than validated against the fragment; the extension fields themselves follow the definitions below. Extension fields are additive — a valid CEM remains valid without them.

{
  "schemaVersion": "1.0.0",
  "modules": [
    {
      "kind": "javascript-module",
      "path": "src/lasagna-button.js",
      "declarations": [
        {
          "kind": "class",
          "name": "LasagnaButton",
          "tagName": "lasagna-button",
          "status": "deprecated",
          "deprecated": "Use “lasagna-action-button” instead.",
          "attributes": [
            {
              "name": "variant",
              "enum": [
                "primary",
                "ghost"
              ],
              "deprecatedValues": [
                {
                  "value": "flat",
                  "message": "Use “ghost” instead."
                }
              ]
            }
          ]
        }
      ]
    }
  ]
}

Lifecycle fields

The LifecycleFields definition is the composable set of optional lifecycle fields a design system may add to a CEM entry. The alias definitions below apply it at declaration, member, slot, cssProperty, cssPart, and event scope.

{
  "deprecated": "Use \"lasagna-action-button\" instead."
}

{
  "status": "deprecated"
}

{
  "removal": "2026-07-01"
}

{
  "replacement": "lasagna-action-button"
}

Attribute extensions

The AttributeExtensions definition extends a CEM attribute entry with its allowed value set, attribute-level lifecycle fields, and per-value deprecation records. Attribute-level lifecycle and deprecatedValues are independent axes.

{
  "enum": [
    "primary",
    "ghost"
  ]
}

{
  "deprecated": "Use the variant attribute instead."
}

{
  "status": "stable"
}

{
  "removal": "3.0.0"
}

{
  "replacement": "lasagna-button-lg"
}

{
  "deprecatedValues": [
    {
      "value": "flat",
      "message": "Use \"ghost\" instead."
    }
  ]
}

Nested definitions

Reusable shapes referenced by the fields above.