diff --git a/gradle.properties b/gradle.properties
index 648ab2dfe4..2ccf1653b8 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -8,7 +8,7 @@ android.useAndroidX=true
 systemProp.org.gradle.internal.publish.checksums.insecure=true
 
 GROUP=com.squareup.workflow1
-VERSION_NAME=1.8.0-uiUpdate03-SNAPSHOT
+VERSION_NAME=1.8.0-uiUpdate04-SNAPSHOT
 
 POM_DESCRIPTION=Square Workflow
 
diff --git a/workflow-ui/core-android/api/core-android.api b/workflow-ui/core-android/api/core-android.api
index fff19b9e8f..977407be60 100644
--- a/workflow-ui/core-android/api/core-android.api
+++ b/workflow-ui/core-android/api/core-android.api
@@ -199,7 +199,12 @@ public abstract interface class com/squareup/workflow1/ui/ScreenViewHolder {
 }
 
 public final class com/squareup/workflow1/ui/ScreenViewHolder$Companion {
-	public final fun getShowing ()Lcom/squareup/workflow1/ui/ViewEnvironmentKey;
+}
+
+public final class com/squareup/workflow1/ui/ScreenViewHolder$Companion$Showing : com/squareup/workflow1/ui/ViewEnvironmentKey {
+	public static final field INSTANCE Lcom/squareup/workflow1/ui/ScreenViewHolder$Companion$Showing;
+	public fun getDefault ()Lcom/squareup/workflow1/ui/Screen;
+	public synthetic fun getDefault ()Ljava/lang/Object;
 }
 
 public final class com/squareup/workflow1/ui/ScreenViewHolder$Companion$ShowingNothing : com/squareup/workflow1/ui/Screen {
diff --git a/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/ScreenViewHolder.kt b/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/ScreenViewHolder.kt
index b016f869f8..45136e3ea4 100644
--- a/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/ScreenViewHolder.kt
+++ b/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/ScreenViewHolder.kt
@@ -44,7 +44,9 @@ public interface ScreenViewHolder<in ScreenT : Screen> {
      * Provides access to the [Screen] instance most recently shown in a [ScreenViewHolder]'s
      * [view] via [show]. Call [showing] for more convenient access.
      */
-    public val Showing: ViewEnvironmentKey<Screen> = ViewEnvironmentKey { ShowingNothing }
+    public object Showing : ViewEnvironmentKey<Screen>(Screen::class) {
+      override val default: Screen = ShowingNothing
+    }
   }
 }
 
diff --git a/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/BackStackContainer.kt b/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/BackStackContainer.kt
index 0e179d5fbc..d3ba0f948c 100644
--- a/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/BackStackContainer.kt
+++ b/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/BackStackContainer.kt
@@ -20,6 +20,7 @@ import com.squareup.workflow1.ui.Compatible.Companion.keyFor
 import com.squareup.workflow1.ui.NamedScreen
 import com.squareup.workflow1.ui.R
 import com.squareup.workflow1.ui.ScreenViewHolder
+import com.squareup.workflow1.ui.ScreenViewHolder.Companion.Showing
 import com.squareup.workflow1.ui.ViewEnvironment
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
 import com.squareup.workflow1.ui.androidx.WorkflowAndroidXSupport.stateRegistryOwnerFromViewTreeOrContext
@@ -65,7 +66,7 @@ public open class BackStackContainer @JvmOverloads constructor(
     newRendering: BackStackScreen<*>,
     newViewEnvironment: ViewEnvironment
   ) {
-    savedStateParentKey = keyFor(newViewEnvironment[ScreenViewHolder.Showing])
+    savedStateParentKey = keyFor(newViewEnvironment[Showing])
 
     val config = if (newRendering.backStack.isEmpty()) First else Other
     val environment = newViewEnvironment + config
diff --git a/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/BodyAndModalsContainer.kt b/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/BodyAndModalsContainer.kt
index 486049a36d..9fdc00c010 100644
--- a/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/BodyAndModalsContainer.kt
+++ b/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/BodyAndModalsContainer.kt
@@ -17,6 +17,7 @@ import com.squareup.workflow1.ui.Compatible.Companion.keyFor
 import com.squareup.workflow1.ui.R
 import com.squareup.workflow1.ui.ScreenViewFactory
 import com.squareup.workflow1.ui.ScreenViewHolder
+import com.squareup.workflow1.ui.ScreenViewHolder.Companion.Showing
 import com.squareup.workflow1.ui.ViewEnvironment
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
 import com.squareup.workflow1.ui.WorkflowViewStub
@@ -82,7 +83,7 @@ internal class BodyAndModalsContainer @JvmOverloads constructor(
     newScreen: BodyAndModalsScreen<*, *>,
     viewEnvironment: ViewEnvironment
   ) {
-    savedStateParentKey = keyFor(viewEnvironment[ScreenViewHolder.Showing])
+    savedStateParentKey = keyFor(viewEnvironment[Showing])
 
     val showingModals = newScreen.modals.isNotEmpty()
 
diff --git a/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreenLegacyViewFactory.kt b/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreenLegacyViewFactory.kt
index 1cf55202a7..e568c047be 100644
--- a/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreenLegacyViewFactory.kt
+++ b/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreenLegacyViewFactory.kt
@@ -5,7 +5,6 @@ package com.squareup.workflow1.ui.container
 import com.squareup.workflow1.ui.DecorativeViewFactory
 import com.squareup.workflow1.ui.ViewFactory
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
-import com.squareup.workflow1.ui.merge
 
 @Suppress("DEPRECATION")
 @WorkflowUiExperimentalApi
@@ -13,6 +12,6 @@ internal object EnvironmentScreenLegacyViewFactory : ViewFactory<EnvironmentScre
 by DecorativeViewFactory(
   type = EnvironmentScreen::class,
   map = { environmentScreen, inheritedEnvironment ->
-    Pair(environmentScreen.wrapped, environmentScreen.environment merge inheritedEnvironment)
+    Pair(environmentScreen.wrapped, environmentScreen.environment + inheritedEnvironment)
   }
 )
diff --git a/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreenViewFactory.kt b/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreenViewFactory.kt
index 46612e67ae..b139451644 100644
--- a/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreenViewFactory.kt
+++ b/workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreenViewFactory.kt
@@ -4,7 +4,6 @@ import com.squareup.workflow1.ui.Screen
 import com.squareup.workflow1.ui.ScreenViewFactory
 import com.squareup.workflow1.ui.ScreenViewFactory.Companion.fromCode
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
-import com.squareup.workflow1.ui.merge
 import com.squareup.workflow1.ui.toUnwrappingViewFactory
 import com.squareup.workflow1.ui.toViewFactory
 
@@ -12,13 +11,13 @@ import com.squareup.workflow1.ui.toViewFactory
 internal fun <WrappedT : Screen> EnvironmentScreenViewFactory():
   ScreenViewFactory<EnvironmentScreen<WrappedT>> {
   return fromCode { initialEnvScreen, initialEnvironment, context, container ->
-    val mergedInitialEnvironment = initialEnvironment merge initialEnvScreen.environment
+    val mergedInitialEnvironment = initialEnvironment + initialEnvScreen.environment
 
     initialEnvScreen.wrapped.toViewFactory(mergedInitialEnvironment)
       .toUnwrappingViewFactory<EnvironmentScreen<WrappedT>, WrappedT>(
         unwrap = { it.wrapped },
         showWrapperScreen = { _, envScreen, environment, showUnwrapped ->
-          showUnwrapped(envScreen.wrapped, environment merge envScreen.environment)
+          showUnwrapped(envScreen.wrapped, environment + envScreen.environment)
         }
       )
       .buildView(initialEnvScreen, mergedInitialEnvironment, context, container)
diff --git a/workflow-ui/core-common/api/core-common.api b/workflow-ui/core-common/api/core-common.api
index f18bf4368d..fc5a31fe09 100644
--- a/workflow-ui/core-common/api/core-common.api
+++ b/workflow-ui/core-common/api/core-common.api
@@ -102,14 +102,11 @@ public final class com/squareup/workflow1/ui/ViewEnvironment$Companion {
 
 public abstract class com/squareup/workflow1/ui/ViewEnvironmentKey {
 	public fun <init> (Lkotlin/reflect/KClass;)V
+	public fun combine (Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
 	public final fun equals (Ljava/lang/Object;)Z
 	public abstract fun getDefault ()Ljava/lang/Object;
 	public final fun hashCode ()I
-	public fun toString ()Ljava/lang/String;
-}
-
-public final class com/squareup/workflow1/ui/ViewEnvironmentKt {
-	public static final synthetic fun ViewEnvironmentKey (Lkotlin/jvm/functions/Function0;)Lcom/squareup/workflow1/ui/ViewEnvironmentKey;
+	public final fun toString ()Ljava/lang/String;
 }
 
 public abstract interface class com/squareup/workflow1/ui/ViewRegistry {
@@ -119,6 +116,8 @@ public abstract interface class com/squareup/workflow1/ui/ViewRegistry {
 }
 
 public final class com/squareup/workflow1/ui/ViewRegistry$Companion : com/squareup/workflow1/ui/ViewEnvironmentKey {
+	public fun combine (Lcom/squareup/workflow1/ui/ViewRegistry;Lcom/squareup/workflow1/ui/ViewRegistry;)Lcom/squareup/workflow1/ui/ViewRegistry;
+	public synthetic fun combine (Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
 	public fun getDefault ()Lcom/squareup/workflow1/ui/ViewRegistry;
 	public synthetic fun getDefault ()Ljava/lang/Object;
 }
@@ -131,8 +130,6 @@ public final class com/squareup/workflow1/ui/ViewRegistryKt {
 	public static final fun ViewRegistry ()Lcom/squareup/workflow1/ui/ViewRegistry;
 	public static final fun ViewRegistry ([Lcom/squareup/workflow1/ui/ViewRegistry$Entry;)Lcom/squareup/workflow1/ui/ViewRegistry;
 	public static final synthetic fun get (Lcom/squareup/workflow1/ui/ViewRegistry;Lkotlin/reflect/KClass;)Lcom/squareup/workflow1/ui/ViewRegistry$Entry;
-	public static final fun merge (Lcom/squareup/workflow1/ui/ViewEnvironment;Lcom/squareup/workflow1/ui/ViewEnvironment;)Lcom/squareup/workflow1/ui/ViewEnvironment;
-	public static final fun merge (Lcom/squareup/workflow1/ui/ViewEnvironment;Lcom/squareup/workflow1/ui/ViewRegistry;)Lcom/squareup/workflow1/ui/ViewEnvironment;
 	public static final fun merge (Lcom/squareup/workflow1/ui/ViewRegistry;Lcom/squareup/workflow1/ui/ViewRegistry;)Lcom/squareup/workflow1/ui/ViewRegistry;
 	public static final fun plus (Lcom/squareup/workflow1/ui/ViewEnvironment;Lcom/squareup/workflow1/ui/ViewRegistry;)Lcom/squareup/workflow1/ui/ViewEnvironment;
 	public static final fun plus (Lcom/squareup/workflow1/ui/ViewRegistry;Lcom/squareup/workflow1/ui/ViewRegistry$Entry;)Lcom/squareup/workflow1/ui/ViewRegistry;
diff --git a/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/ViewEnvironment.kt b/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/ViewEnvironment.kt
index 3a51ff3105..bb7d084928 100644
--- a/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/ViewEnvironment.kt
+++ b/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/ViewEnvironment.kt
@@ -19,19 +19,30 @@ public class ViewEnvironment
 constructor(
   public val map: Map<ViewEnvironmentKey<*>, Any> = emptyMap()
 ) {
-  @Suppress("UNCHECKED_CAST")
-  public operator fun <T : Any> get(key: ViewEnvironmentKey<T>): T = map[key] as? T ?: key.default
+  public operator fun <T : Any> get(key: ViewEnvironmentKey<T>): T = getOrNull(key) ?: key.default
 
-  @Suppress("DEPRECATION")
-  public operator fun <T : Any> plus(pair: Pair<ViewEnvironmentKey<T>, T>): ViewEnvironment =
-    ViewEnvironment(map + pair)
+  public operator fun <T : Any> plus(pair: Pair<ViewEnvironmentKey<T>, T>): ViewEnvironment {
+    val (newKey, newValue) = pair
+    val newPair = getOrNull(newKey)
+      ?.let { oldValue -> newKey to newKey.combine(oldValue, newValue) }
+      ?: pair
+    @Suppress("DEPRECATION")
+    return ViewEnvironment(map + newPair)
+  }
 
   @Suppress("DEPRECATION")
   public operator fun plus(other: ViewEnvironment): ViewEnvironment {
     if (this == other) return this
     if (other.map.isEmpty()) return this
-    if (this.map.isEmpty()) return other
-    return ViewEnvironment(map + other.map)
+    if (map.isEmpty()) return other
+    val newMap = map.toMutableMap()
+    other.map.entries.forEach { (key, value) ->
+      @Suppress("UNCHECKED_CAST")
+      newMap[key] = getOrNull(key as ViewEnvironmentKey<Any>)
+        ?.let { oldValue -> key.combine(oldValue, value) }
+        ?: value
+    }
+    return ViewEnvironment(newMap)
   }
 
   override fun toString(): String = "ViewEnvironment($map)"
@@ -41,6 +52,9 @@ constructor(
 
   override fun hashCode(): Int = map.hashCode()
 
+  @Suppress("UNCHECKED_CAST")
+  private fun <T : Any> getOrNull(key: ViewEnvironmentKey<T>): T? = map[key] as? T
+
   public companion object {
     @Suppress("DEPRECATION")
     public val EMPTY: ViewEnvironment = ViewEnvironment()
@@ -57,6 +71,15 @@ public abstract class ViewEnvironmentKey<T : Any>(
 ) {
   public abstract val default: T
 
+  /**
+   * Applied from [ViewEnvironment.plus] when the receiving environment already contains
+   * a value for this key. The default implementation replaces [left] with [right].
+   */
+  public open fun combine(
+    left: T,
+    right: T
+  ): T = right
+
   final override fun equals(other: Any?): Boolean = when {
     this === other -> true
     other != null && this::class != other::class -> false
@@ -65,17 +88,7 @@ public abstract class ViewEnvironmentKey<T : Any>(
 
   final override fun hashCode(): Int = type.hashCode()
 
-  override fun toString(): String {
+  final override fun toString(): String {
     return "${this::class.simpleName}(${type.simpleName})"
   }
 }
-
-@WorkflowUiExperimentalApi
-public inline fun <reified T : Any> ViewEnvironmentKey(
-  crossinline produceDefault: () -> T,
-): ViewEnvironmentKey<T> {
-  return object : ViewEnvironmentKey<T>(T::class) {
-    override val default: T
-      get() = produceDefault()
-  }
-}
diff --git a/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/ViewRegistry.kt b/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/ViewRegistry.kt
index 987ce84f40..d90d37ab0a 100644
--- a/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/ViewRegistry.kt
+++ b/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/ViewRegistry.kt
@@ -83,6 +83,10 @@ public interface ViewRegistry {
 
   public companion object : ViewEnvironmentKey<ViewRegistry>(ViewRegistry::class) {
     override val default: ViewRegistry get() = ViewRegistry()
+    override fun combine(
+      left: ViewRegistry,
+      right: ViewRegistry
+    ): ViewRegistry = left.merge(right)
   }
 }
 
@@ -103,13 +107,17 @@ public fun ViewRegistry(vararg bindings: Entry<*>): ViewRegistry =
 public fun ViewRegistry(): ViewRegistry = TypedViewRegistry()
 
 /**
- *  @throws IllegalArgumentException if the receiver already has a matching [entry].
+ * Transforms the receiver to add [entry], throwing [IllegalArgumentException] if the receiver
+ * already has a matching [entry]. Use [merge] to replace an existing entry with a new one.
  */
 @WorkflowUiExperimentalApi
 public operator fun ViewRegistry.plus(entry: Entry<*>): ViewRegistry =
   this + ViewRegistry(entry)
 
-/** @throws IllegalArgumentException if other has redundant entries. */
+/**
+ * Transforms the receiver to add all entries from [other], throwing [IllegalArgumentException]
+ * if the receiver already has any matching [entry]. Use [merge] to replace existing entries.
+ */
 @WorkflowUiExperimentalApi
 public operator fun ViewRegistry.plus(other: ViewRegistry): ViewRegistry {
   if (other.keys.isEmpty()) return this
@@ -117,10 +125,6 @@ public operator fun ViewRegistry.plus(other: ViewRegistry): ViewRegistry {
   return CompositeViewRegistry(this, other)
 }
 
-/**
- * Replaces the existing [ViewRegistry] of the receiver with [registry]. Use
- * [ViewEnvironment.merge] to combine them instead.
- */
 @WorkflowUiExperimentalApi
 public operator fun ViewEnvironment.plus(registry: ViewRegistry): ViewEnvironment {
   if (this[ViewRegistry] === registry) return this
@@ -144,32 +148,3 @@ public infix fun ViewRegistry.merge(other: ViewRegistry): ViewRegistry {
     .toTypedArray()
     .let { ViewRegistry(*it) }
 }
-
-/**
- * Merges the [ViewRegistry] of the receiver with [registry]. If there are conflicting entries,
- * those in [registry] are preferred.
- */
-@WorkflowUiExperimentalApi
-public infix fun ViewEnvironment.merge(registry: ViewRegistry): ViewEnvironment {
-  if (this[ViewRegistry] === registry) return this
-  if (registry.keys.isEmpty()) return this
-
-  val merged = this[ViewRegistry] merge registry
-  return this + merged
-}
-
-/**
- * Combines the receiving [ViewEnvironment] with [other], taking care to merge
- * their [ViewRegistry] entries. Any other conflicting values in [other] replace those
- * in the receiver.
- */
-@WorkflowUiExperimentalApi
-public infix fun ViewEnvironment.merge(other: ViewEnvironment): ViewEnvironment {
-  if (this == other) return this
-  if (other.map.isEmpty()) return this
-  if (this.map.isEmpty()) return other
-
-  val oldReg = this[ViewRegistry]
-  val newReg = other[ViewRegistry]
-  return this + other + (ViewRegistry to oldReg.merge(newReg))
-}
diff --git a/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreen.kt b/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreen.kt
index e724491ba8..7d73579e10 100644
--- a/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreen.kt
+++ b/workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/container/EnvironmentScreen.kt
@@ -5,7 +5,7 @@ import com.squareup.workflow1.ui.Screen
 import com.squareup.workflow1.ui.ViewEnvironment
 import com.squareup.workflow1.ui.ViewRegistry
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
-import com.squareup.workflow1.ui.merge
+import com.squareup.workflow1.ui.plus
 
 /**
  * Pairs a [wrapped] rendering with a [environment] to support its display.
@@ -36,7 +36,7 @@ public class EnvironmentScreen<V : Screen>(
  */
 @WorkflowUiExperimentalApi
 public fun Screen.withRegistry(viewRegistry: ViewRegistry): EnvironmentScreen<*> {
-  return withEnvironment(ViewEnvironment.EMPTY merge viewRegistry)
+  return withEnvironment(ViewEnvironment.EMPTY + viewRegistry)
 }
 
 /**
@@ -53,7 +53,7 @@ public fun Screen.withEnvironment(
   return when (this) {
     is EnvironmentScreen<*> -> {
       if (environment.map.isEmpty()) this
-      else EnvironmentScreen(wrapped, this.environment merge environment)
+      else EnvironmentScreen(wrapped, this.environment + environment)
     }
     else -> EnvironmentScreen(this, environment)
   }
diff --git a/workflow-ui/core-common/src/test/java/com/squareup/workflow1/ui/ViewEnvironmentTest.kt b/workflow-ui/core-common/src/test/java/com/squareup/workflow1/ui/ViewEnvironmentTest.kt
index 9b2499ba77..063aee10f3 100644
--- a/workflow-ui/core-common/src/test/java/com/squareup/workflow1/ui/ViewEnvironmentTest.kt
+++ b/workflow-ui/core-common/src/test/java/com/squareup/workflow1/ui/ViewEnvironmentTest.kt
@@ -99,4 +99,22 @@ internal class ViewEnvironmentTest {
     val environment = EMPTY + (StringHint to "able")
     assertThat(environment + environment).isSameInstanceAs(environment)
   }
+
+  @Test fun `honors combine`() {
+    val combiningHint = object : ViewEnvironmentKey<String>(String::class) {
+      override val default: String
+        get() = error("")
+
+      override fun combine(
+        left: String,
+        right: String
+      ): String {
+        return "$left-$right"
+      }
+    }
+
+    val left = EMPTY + (combiningHint to "able")
+    val right = EMPTY + (combiningHint to "baker")
+    assertThat((left + right)[combiningHint]).isEqualTo("able-baker")
+  }
 }
diff --git a/workflow-ui/core-common/src/test/java/com/squareup/workflow1/ui/ViewRegistryTest.kt b/workflow-ui/core-common/src/test/java/com/squareup/workflow1/ui/ViewRegistryTest.kt
index eff9e68b19..45b1b7c327 100644
--- a/workflow-ui/core-common/src/test/java/com/squareup/workflow1/ui/ViewRegistryTest.kt
+++ b/workflow-ui/core-common/src/test/java/com/squareup/workflow1/ui/ViewRegistryTest.kt
@@ -60,22 +60,27 @@ internal class ViewRegistryTest {
     assertThat(merged[FooRendering::class]).isSameInstanceAs(factory2)
   }
 
-  @Test fun `merge into ViewEnvironment prefers right side`() {
-    val factory1 = TestEntry(FooRendering::class)
-    val factory2 = TestEntry(FooRendering::class)
-    val merged = (EMPTY + ViewRegistry(factory1)) merge ViewRegistry(factory2)
+  @Test fun `ViewEnvironment plus ViewRegistry prefers new registry values`() {
+    val leftBar = TestEntry(BarRendering::class)
+    val rightBar = TestEntry(BarRendering::class)
+
+    val env = EMPTY + ViewRegistry(leftBar)
+    val merged = env + ViewRegistry(rightBar, TestEntry(FooRendering::class))
 
-    assertThat(merged[ViewRegistry][FooRendering::class]).isSameInstanceAs(factory2)
+    assertThat(merged[ViewRegistry][BarRendering::class]).isSameInstanceAs(rightBar)
+    assertThat(merged[ViewRegistry][FooRendering::class]).isNotNull()
   }
 
-  @Test fun `merge of ViewEnvironments prefers right side`() {
-    val factory1 = TestEntry(FooRendering::class)
-    val factory2 = TestEntry(FooRendering::class)
-    val e1 = EMPTY + ViewRegistry(factory1)
-    val e2 = EMPTY + ViewRegistry(factory2)
-    val merged = e1 + e2
+  @Test fun `ViewEnvironment plus ViewEnvironment prefers right ViewRegistry`() {
+    val leftBar = TestEntry(BarRendering::class)
+    val rightBar = TestEntry(BarRendering::class)
+
+    val leftEnv = EMPTY + ViewRegistry(leftBar)
+    val rightEnv = EMPTY + ViewRegistry(rightBar, TestEntry(FooRendering::class))
+    val merged = leftEnv + rightEnv
 
-    assertThat(merged[ViewRegistry][FooRendering::class]).isSameInstanceAs(factory2)
+    assertThat(merged[ViewRegistry][BarRendering::class]).isSameInstanceAs(rightBar)
+    assertThat(merged[ViewRegistry][FooRendering::class]).isNotNull()
   }
 
   @Test fun `plus of empty returns this`() {
@@ -98,21 +103,6 @@ internal class ViewRegistryTest {
     assertThat(ViewRegistry() merge reg).isSameInstanceAs(reg)
   }
 
-  @Test fun `env merge of empty reg returns this env`() {
-    val env = EMPTY + ViewRegistry(TestEntry(FooRendering::class))
-    assertThat(env merge ViewRegistry()).isSameInstanceAs(env)
-  }
-
-  @Test fun `env merge of empty env returns other env`() {
-    val env = EMPTY + ViewRegistry(TestEntry(FooRendering::class))
-    assertThat(env merge EMPTY).isSameInstanceAs(env)
-  }
-
-  @Test fun `env merge to empty env returns other env`() {
-    val env = EMPTY + ViewRegistry(TestEntry(FooRendering::class))
-    assertThat(EMPTY merge env).isSameInstanceAs(env)
-  }
-
   @Test fun `env plus empty reg returns env`() {
     val env = EMPTY + ViewRegistry(TestEntry(FooRendering::class))
     assertThat(env + ViewRegistry()).isSameInstanceAs(env)
@@ -136,17 +126,6 @@ internal class ViewRegistryTest {
     assertThat(reg merge reg).isSameInstanceAs(reg)
   }
 
-  @Test fun `env merges same reg returns self`() {
-    val reg = ViewRegistry(TestEntry(FooRendering::class))
-    val env = EMPTY + reg
-    assertThat(env merge reg).isSameInstanceAs(env)
-  }
-
-  @Test fun `env merges self reg returns self`() {
-    val env = EMPTY + ViewRegistry(TestEntry(FooRendering::class))
-    assertThat(env merge env).isSameInstanceAs(env)
-  }
-
   private class TestEntry<T : Any>(
     override val type: KClass<in T>
   ) : Entry<T>