diff --git a/app/controllers/catalog_controller.rb b/app/controllers/catalog_controller.rb
index 012181aa..7ede2239 100644
--- a/app/controllers/catalog_controller.rb
+++ b/app/controllers/catalog_controller.rb
@@ -43,6 +43,8 @@ def unique_custom_fields
     config.browse.document_actions = config.index.document_actions
 
     ## Default parameters to send to solr for all search-like requests. See also SolrHelper#solr_search_params
+    # Group records by manifest in order to display a single result for a given
+    # resource in 'search across'
     config.default_solr_params = {
       qt: 'search',
       rows: 10,
diff --git a/app/models/adjusted_grouped_response.rb b/app/models/adjusted_grouped_response.rb
index 2f415360..599df418 100644
--- a/app/models/adjusted_grouped_response.rb
+++ b/app/models/adjusted_grouped_response.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+# After the grouping that happens during search, the facet counts are wrong. We
+# adjust them to reflect actual counts for the result set.
 class AdjustedGroupedResponse < Blacklight::Solr::Response
   def initialize(*args)
     data = FacetCount.new(args.first)
diff --git a/architecture-decisions/0005-resource-per-collection.md b/architecture-decisions/0005-resource-per-collection.md
new file mode 100644
index 00000000..2f771b90
--- /dev/null
+++ b/architecture-decisions/0005-resource-per-collection.md
@@ -0,0 +1,35 @@
+# 5. Create a IIIFResource for each Collection that a resource is a member of
+
+Date: Archaeological
+
+## Status
+
+Accepted
+
+## Context
+
+We needed to be able to display a resource in more than one collection, because
+in Figgy a resource can be a member of multiple collections.
+
+At the time of this decision, one IIIFResource could only be a member of one Exhibit.
+
+## Decision
+
+We create one IIIFResource per Collection of which it is a member.
+
+We map each IIIFResource to one SolrDocument.
+
+## Consequences
+
+* 'Search Across' requires a complicated grouping mechanism (in solr) in order
+  to keep a resource from appearing multiple times.
+
+* It's easy to delete a collection and all its resources. It's easy to delete a
+  resource if it's no longer in a given collection.
+
+* The resource that appears in 'Search Across' displays metadata as shown in the
+  exhibit it happened to pull the resource from. This may be be specialized to
+  the exhibit, and different from the canonical data as stored in figgy.
+
+* If spotlight introduces the ability to have one resource in multiple exhibits
+  we may have a different implementation than is in core (this happened).