diff --git a/smack-experimental/src/main/java/org/jivesoftware/smackx/mix/core/MixChannel.java b/smack-experimental/src/main/java/org/jivesoftware/smackx/mix/core/MixChannel.java
new file mode 100644
index 000000000..34d586d84
--- /dev/null
+++ b/smack-experimental/src/main/java/org/jivesoftware/smackx/mix/core/MixChannel.java
@@ -0,0 +1,5 @@
+package org.jivesoftware.smackx.mix.core;
+
+public class MixChannel {
+
+}
diff --git a/smack-experimental/src/main/java/org/jivesoftware/smackx/mix/core/MixParticipant.java b/smack-experimental/src/main/java/org/jivesoftware/smackx/mix/core/MixParticipant.java
new file mode 100644
index 000000000..730d85c2c
--- /dev/null
+++ b/smack-experimental/src/main/java/org/jivesoftware/smackx/mix/core/MixParticipant.java
@@ -0,0 +1,26 @@
+package org.jivesoftware.smackx.mix.core;
+
+import org.jxmpp.jid.EntityBareJid;
+
+public class MixParticipant {
+
+    private EntityBareJid jid;
+    private String nick;
+
+    public MixParticipant(EntityBareJid jid) {
+        this(jid, null);
+    }
+
+    public MixParticipant(EntityBareJid jid, String nick) {
+        this.jid = jid;
+        this.nick = nick;
+    }
+
+    public EntityBareJid getJid() {
+        return jid;
+    }
+
+    public String getNick() {
+        return nick;
+    }
+}
diff --git a/smack-experimental/src/main/java/org/jivesoftware/smackx/mix/core/StableParticipantId.java b/smack-experimental/src/main/java/org/jivesoftware/smackx/mix/core/StableParticipantId.java
new file mode 100644
index 000000000..2a8ec187f
--- /dev/null
+++ b/smack-experimental/src/main/java/org/jivesoftware/smackx/mix/core/StableParticipantId.java
@@ -0,0 +1,68 @@
+package org.jivesoftware.smackx.mix.core;
+
+import java.util.stream.IntStream;
+
+import org.jivesoftware.smack.util.StringUtils;
+
+public final class StableParticipantId implements CharSequence {
+
+    private final String id;
+
+    private StableParticipantId(String string) {
+        String id = StringUtils.requireNotNullNorEmpty(string.trim(),
+                "Stable Participant ID MUST NOT be null, nor empty.");
+        if (id.contains("#") || id.contains("/") || id.contains("@")) {
+            throw new IllegalArgumentException("Stable Participant ID MUST NOT contain the '#', '/' or '@' characters.");
+        }
+        this.id = id;
+    }
+
+    @Override
+    public int length() {
+        return id.length();
+    }
+
+    @Override
+    public char charAt(int i) {
+        return id.charAt(i);
+    }
+
+    @Override
+    public CharSequence subSequence(int i, int i1) {
+        return id.subSequence(i, i1);
+    }
+
+    @Override
+    public IntStream chars() {
+        return id.chars();
+    }
+
+    @Override
+    public IntStream codePoints() {
+        return id.codePoints();
+    }
+
+    @Override
+    public int hashCode() {
+        return id.hashCode();
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (obj == null) {
+            return false;
+        }
+        if (this == obj) {
+            return true;
+        }
+        if (!(obj instanceof StableParticipantId)) {
+            return false;
+        }
+        return toString().equals(((StableParticipantId) obj).toString());
+    }
+
+    @Override
+    public String toString() {
+        return id;
+    }
+}
diff --git a/smack-experimental/src/test/java/org/jivesoftware/smackx/mix/core/provider/LeaveElementProviderTest.java b/smack-experimental/src/test/java/org/jivesoftware/smackx/mix/core/provider/LeaveElementProviderTest.java
index 24c2dcd27..51dca0315 100644
--- a/smack-experimental/src/test/java/org/jivesoftware/smackx/mix/core/provider/LeaveElementProviderTest.java
+++ b/smack-experimental/src/test/java/org/jivesoftware/smackx/mix/core/provider/LeaveElementProviderTest.java
@@ -17,7 +17,6 @@
 package org.jivesoftware.smackx.mix.core.provider;
 
 import static org.junit.jupiter.api.Assertions.assertNotNull;
-import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.IOException;
 
@@ -40,6 +39,5 @@ public class LeaveElementProviderTest {
         LeaveElement element = provider.parse(parser);
 
         assertNotNull(element);
-        assertTrue(element instanceof LeaveElement.V1);
     }
 }