Defaults vs overrides

9. Defaults vs Overrides

When to Use

When deciding whether to allow per-entity layout customization or use a single default layout for all entities of a bundle.

Decision

If you need...	Use...	Why
Same layout for all entities of bundle	Defaults only (allow_custom: false)	Single source of truth, easy to update all entities, config-based deployment
Per-entity unique layouts	Overrides enabled (allow_custom: true)	Editors can customize individual entity layouts, content stored in entity field
Mix of standard and custom layouts	Defaults with selective overrides	Most entities use default, special entities override as needed
Staging/production parity	Defaults only	Config export/import, no content dependencies for layout structure
Content-driven layout decisions	Overrides	Layout decisions per entity, possibly based on content strategy or editor preference

Pattern

Defaults only:

# core.entity_view_display.node.article.default.yml
third_party_settings:
  layout_builder:
    enabled: true
    allow_custom: false
    sections:
      - layout_id: layout_twocol_section
        layout_settings: {  }
        components:
          - uuid: abc-123
            region: first
            configuration:
              id: 'field_block:node:article:body'
            weight: 0

With overrides enabled:

third_party_settings:
  layout_builder:
    enabled: true
    allow_custom: true  # Allows per-entity customization
    sections:
      # Default sections for entities without overrides
      - layout_id: layout_onecol
        components: []

When overrides enabled, entities get a layout_builder__layout field (or similar, configurable name) storing per-entity sections.

Reference: /core/modules/layout_builder/src/Plugin/SectionStorage/DefaultsSectionStorage.php and OverridesSectionStorage.php for implementation.

The allow_custom editorial-posture spectrum

allow_custom is not just a boolean — combined with restrictions and Layout Builder Styles it yields three editorial postures:

Posture	Config	Editor experience	Best for
Locked / templated	`allow_custom: false`	Cannot customize; default-only layout	Consistency-critical bundles
Curated	`allow_custom: true` + restrictions allowlist + curated LB Styles	Composes from an approved palette	Most editorial bundles
Open	`allow_custom: true`, no restrictions	Full freedom	Rare / risky

Verified: one production site ran a templated bundle (allow_custom: false) alongside curated bundles (allow_custom: true + per-bundle allowlists) in the same install — the posture is a per-bundle decision, not a site-wide one.

Decision Points

At this point...	If...	Then...
Initial setup	Content editors need flexibility	Enable overrides, but provide good defaults as starting point
Initial setup	Layouts should be controlled/consistent	Defaults only, use Views or other tools for content variation
Default changes	Some entities overridden	Changes only affect non-overridden entities (overrides don't inherit updates)
Default changes	No overrides exist	Changes apply immediately to all entities
Content migration	Overrides enabled	Decide whether migrated entities use default or import custom layouts
Multisite deployment	Overrides in use	Content sync required (not just config), increases deployment complexity

Common Mistakes

Enabling overrides by default → Creates maintenance burden. Changing defaults doesn't update overridden entities. Start with defaults only
Not communicating override behavior → Editors expect layout changes to apply everywhere. Once entity overridden, it's disconnected from defaults — document this clearly
Forgetting override permission → Overrides need separate permission: "Configure editable {entity_type} {bundle} layout overrides". Editors frustrated when can't edit
Not planning for default updates → With overrides, no easy way to push default changes to overridden entities. Either accept divergence or manually update/revert
Mixing content and config → Defaults are config (exportable). Overrides are content (in entity field). Config-only deployment workflows break with overrides
Ignoring revert workflows → Once overridden, only way back to default is "Revert to defaults" button (blows away custom content). No partial revert
Assuming overrides are per-field → Overrides are all-or-nothing for the entire layout. Can't override just one section