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diff --git a/runtime/commonMain/src/kotlinx/serialization/modules/SerialModule.kt b/runtime/commonMain/src/kotlinx/serialization/modules/SerialModule.kt
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+++ b/runtime/commonMain/src/kotlinx/serialization/modules/SerialModule.kt
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+/*
+ * Copyright 2017-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+@file:Suppress("UNCHECKED_CAST", "RedundantVisibilityModifier")
+
+package kotlinx.serialization.modules
+
+import kotlinx.serialization.*
+import kotlin.reflect.*
+
+/**
+ * [SerialModule] is a collection of serializers used by [ContextSerializer] and [PolymorphicSerializer]
+ * to override or provide serializers at the runtime, whereas at the compile-time they provided by the serialization plugin.
+ *
+ * It can be considered as a map where serializers are found using statically known KClasses.
+ *
+ * To enable runtime resolution of serializers, one of the special annotations must be used on target types
+ * and a serial module with serializers should be used during construction of [SerialFormat].
+ *
+ * @see ContextualSerialization
+ * @see Polymorphic
+ */
+public interface SerialModule {
+
+    /**
+     * Returns a contextual serializer associated with a given [kclass].
+     * This method is used in context-sensitive operations on a property marked with [ContextualSerialization] by a [ContextSerializer]
+     */
+    public fun <T : Any> getContextual(kclass: KClass<T>): KSerializer<T>?
+
+    /**
+     * Returns a polymorphic serializer registered for a class of the given [value] in the scope of [baseClass].
+     */
+    public fun <T : Any> getPolymorphic(baseClass: KClass<T>, value: T): KSerializer<out T>?
+
+    /**
+     * Returns a polymorphic serializer registered for for a [serializedClassName] in the scope of [baseClass].
+     */
+    public fun <T : Any> getPolymorphic(baseClass: KClass<T>, serializedClassName: String): KSerializer<out T>?
+
+    /**
+     * Copies contents of this module to the given [collector].
+     */
+    public fun dumpTo(collector: SerialModuleCollector)
+}
+
+/**
+ * A [SerialModule] which is empty and always returns `null`.
+ */
+public object EmptyModule : SerialModule {
+    public override fun <T : Any> getContextual(kclass: KClass<T>): KSerializer<T>? = null
+    public override fun <T : Any> getPolymorphic(baseClass: KClass<T>, value: T): KSerializer<out T>? = null
+    public override fun <T : Any> getPolymorphic(
+        baseClass: KClass<T>,
+        serializedClassName: String
+    ): KSerializer<out T>? = null
+
+    public override fun dumpTo(collector: SerialModuleCollector) = Unit
+}