diff --git a/docs/api/js-yaml-schema.createinclude.md b/docs/api/js-yaml-schema.createinclude.md
index 0dc67c0..66a37f7 100644
--- a/docs/api/js-yaml-schema.createinclude.md
+++ b/docs/api/js-yaml-schema.createinclude.md
@@ -4,7 +4,7 @@
 
 ## createInclude() function
 
-Instantiate an includer with closure over the provided options.
+Instantiate an include type with a copy of the provided options, returning the include type and its schema setter.
 
 <b>Signature:</b>
 
diff --git a/docs/api/js-yaml-schema.schemaoptions.base.md b/docs/api/js-yaml-schema.schemaoptions.base.md
new file mode 100644
index 0000000..8819ebe
--- /dev/null
+++ b/docs/api/js-yaml-schema.schemaoptions.base.md
@@ -0,0 +1,11 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [@apextoaster/js-yaml-schema](./js-yaml-schema.md) &gt; [SchemaOptions](./js-yaml-schema.schemaoptions.md) &gt; [base](./js-yaml-schema.schemaoptions.base.md)
+
+## SchemaOptions.base property
+
+<b>Signature:</b>
+
+```typescript
+base?: Schema;
+```
diff --git a/docs/api/js-yaml-schema.schemaoptions.include.md b/docs/api/js-yaml-schema.schemaoptions.include.md
index 6ea564b..06339b7 100644
--- a/docs/api/js-yaml-schema.schemaoptions.include.md
+++ b/docs/api/js-yaml-schema.schemaoptions.include.md
@@ -7,5 +7,5 @@
 <b>Signature:</b>
 
 ```typescript
-include: Readonly<IncludeOptions>;
+include: Readonly<Omit<IncludeOptions, 'schema'>>;
 ```
diff --git a/src/type/Include.ts b/src/type/Include.ts
index 34e9379..7f19e76 100644
--- a/src/type/Include.ts
+++ b/src/type/Include.ts
@@ -18,11 +18,15 @@ export interface IncludeOptions {
 }
 
 /**
- * Instantiate an includer with closure over the provided options.
+ * Instantiate an include type with a copy of the provided options,
+ * returning the include type and its schema setter.
+ *
  * @public
  */
 export function createInclude(options: Readonly<IncludeOptions>) {
-  const optionsCopy = {...options};
+  const mutableOptions = {
+    schema: mustCoalesce(options.schema, DEFAULT_SCHEMA),
+  };
 
   const includeType = new YamlType('!include', {
     kind: 'scalar',
@@ -45,7 +49,7 @@ export function createInclude(options: Readonly<IncludeOptions>) {
         return load(options.read(abs, {
           encoding: 'utf-8',
         }), {
-          schema: mustCoalesce(optionsCopy.schema, DEFAULT_SCHEMA),
+          schema: mutableOptions.schema,
         });
       } catch (err) {
         throw new InvalidArgumentError('error including file', err);
@@ -55,7 +59,7 @@ export function createInclude(options: Readonly<IncludeOptions>) {
 
   // callback to avoid circular dependency (type must be created before schema)
   function setSchema(schema: Schema) {
-    optionsCopy.schema = schema;
+    mutableOptions.schema = schema;
   };
 
   return {