diff --git a/experiments/os1.mjs b/experiments/os1.mjs
index f5a028d..88c7a4f 100644
--- a/experiments/os1.mjs
+++ b/experiments/os1.mjs
@@ -2,35 +2,6 @@
 
 import { inspect } from 'node:util';
 
-class Not_Storable_Error extends Error {
-	constructor(data) {
-		const { storage, value, property, id } = data;
-		const type = value === null ? 'null' : typeof value;
-		const location = property ? `property "${property}" of record #${id}` : `record #${id}`;
-		super(`Cannot store value of type "${type}" in ${location}: ${inspect(value)}`);
-		this.data = data;
-	}
-}
-
-class Not_Mutable_Error extends Error {
-	constructor(data) {
-		const { storage, value, property, id } = data;
-		const type = value === null ? 'null' : typeof value;
-		const location = property ? `property "${property}" of record #${id}` : `record #${id}`;
-		super(`Cannot set ${location}: record is immutable (tried to store value of type "${type}": ${inspect(value)})`);
-		this.data = data;
-	}
-}
-
-class No_Such_Object_Index_Error extends Error {
-	constructor(data) {
-		const { storage, property, id } = data;
-		const location = property ? `property "${property}" of record #${id}` : `record #${id}`;
-		super(`Cannot get ${location}: no such record index`);
-		this.data = data;
-	}
-}
-
 
 function load_descriptor({ type, value }, { storage, mutable }) {
 	if (type === 'primitive') {
diff --git a/experiments/res1.mjs b/experiments/res1.mjs
index 06c045b..df90ae9 100644
--- a/experiments/res1.mjs
+++ b/experiments/res1.mjs
@@ -1,13 +1,5 @@
-import { inspect } from 'node:util';
 
-class Item_Unresolvable extends Error {
-	constructor(data) {
-		const { resolver, item } = data;
-		const type = item === null ? 'null' : typeof item;
-		super(`Cannot resolve item ${inspect(item)} of type "${type}" using resolver ${resolver}`);
-		this.data = data;
-	}
-}
+
 
 class Abstract_Resolver {
 	resolve(item) {
@@ -63,3 +55,4 @@ tr.rules.set('string', () => 'World');
 
 console.log(cr.resolve('HELLO'));
 console.log(cr.resolve('hello'));
+console.log(cr.resolve(123));
diff --git a/package-manifest.yaml b/package-manifest.yaml
index 99cad4f..016d1b5 100644
--- a/package-manifest.yaml
+++ b/package-manifest.yaml
@@ -4,3 +4,15 @@ packages:
     documentation: documentation/object-graph-storage
     description: Lightweight persistent storage for structured data.
     version: 0.1.0
+
+  rule-processing:
+    path: source/rule-processing
+    documentation: documentation/rule-processing
+    description: Rule based visitors, transformers, resolvers, processors, operators, aggregators and such.
+    version: 0.1.0
+
+  errors:
+    path: source/errors.mjs
+    documentation: documentation/errors
+    description: Library wide error definitions
+    version: 0.1.0
diff --git a/source/errors.mjs b/source/errors.mjs
new file mode 100644
index 0000000..98d6a00
--- /dev/null
+++ b/source/errors.mjs
@@ -0,0 +1,45 @@
+import { inspect } from 'node:util';
+
+// § GROUP: Resolving errors
+
+export class Item_Unresolvable extends Error {
+	constructor(data) {
+		const { resolver, item } = data;
+		const type = item === null ? 'null' : typeof item;
+		super(`Cannot resolve item ${inspect(item)} of type "${type}" using resolver ${resolver}`);
+		this.data = data;
+	}
+}
+
+
+// § GROUP: Storage errors
+
+export class Not_Storable_Error extends Error {
+	constructor(data) {
+		const { storage, value, property, id } = data;
+		const type = value === null ? 'null' : typeof value;
+		const location = property ? `property "${property}" of record #${id}` : `record #${id}`;
+		super(`Cannot store value of type "${type}" in ${location}: ${inspect(value)}`);
+		this.data = data;
+	}
+}
+
+export class Not_Mutable_Error extends Error {
+	constructor(data) {
+		const { storage, value, property, id } = data;
+		const type = value === null ? 'null' : typeof value;
+		const location = property ? `property "${property}" of record #${id}` : `record #${id}`;
+		super(`Cannot set ${location}: record is immutable (tried to store value of type "${type}": ${inspect(value)})`);
+		this.data = data;
+	}
+}
+
+export class No_Such_Object_Index_Error extends Error {
+	constructor(data) {
+		const { storage, property, id } = data;
+		const location = property ? `property "${property}" of record #${id}` : `record #${id}`;
+		super(`Cannot get ${location}: no such record index`);
+		this.data = data;
+	}
+}
+