diff --git a/core/src/test/java/org/incenp/linkml/core/playground/Bar.java b/core/src/test/java/org/incenp/linkml/core/playground/Bar.java
new file mode 100644
index 0000000..058010c
--- /dev/null
+++ b/core/src/test/java/org/incenp/linkml/core/playground/Bar.java
@@ -0,0 +1,19 @@
+package org.incenp.linkml.core.playground;
+
+/**
+ * An example of a class that is used in a “refined” slot.
+ * <p>
+ * This class is used in the {@link Foo} class. Some of the classes that are
+ * derived from <code>Foo</code> uses derived classes instead.
+ */
+public class Bar {
+    private String name;
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String value) {
+        name = value;
+    }
+}
diff --git a/core/src/test/java/org/incenp/linkml/core/playground/FirstDerivedBar.java b/core/src/test/java/org/incenp/linkml/core/playground/FirstDerivedBar.java
new file mode 100644
index 0000000..e047920
--- /dev/null
+++ b/core/src/test/java/org/incenp/linkml/core/playground/FirstDerivedBar.java
@@ -0,0 +1,20 @@
+package org.incenp.linkml.core.playground;
+
+/**
+ * First derived class from Bar.
+ * <p>
+ * This class is used, instead of its parent <code>Bar</code> in
+ * {@link FirstDerivedFoo}.
+ */
+public class FirstDerivedBar extends Bar {
+
+    private int length;
+
+    public int getLength() {
+        return length;
+    }
+
+    public void setLength(int value) {
+        length = value;
+    }
+}
diff --git a/core/src/test/java/org/incenp/linkml/core/playground/FirstDerivedFoo.java b/core/src/test/java/org/incenp/linkml/core/playground/FirstDerivedFoo.java
new file mode 100644
index 0000000..628ddea
--- /dev/null
+++ b/core/src/test/java/org/incenp/linkml/core/playground/FirstDerivedFoo.java
@@ -0,0 +1,125 @@
+package org.incenp.linkml.core.playground;
+
+import java.util.List;
+
+/**
+ * An example of a class that refines the range of its slots to make them accept
+ * only a more specialised subclass.
+ */
+public class FirstDerivedFoo extends Foo {
+
+    /*
+     * Overridden read accessor for the `bar` slot.
+     * 
+     * We override it to ensure that it returns the more specialised subtype.
+     */
+    @Override
+    public FirstDerivedBar getBar() {
+        // This cast is perfectly safe because the write accessor below guarantees that
+        // only a FirstDerivedBar object can be assigned to the slot.
+        return (FirstDerivedBar) super.getBar();
+    }
+
+    /*
+     * Overridden write accessor for the `bar` slot.
+     * 
+     * We override it to add a runtime check to enforce the more specialised type
+     * constraint. We cannot prevent client code from trying to assign an object of
+     * the wrong type, but if that happens we can at least immediately throw an
+     * exception.
+     */
+    @Override
+    public void setBar(Bar value) {
+        if ( !(value instanceof FirstDerivedBar) ) {
+            throw new IllegalArgumentException("Invalid bar value");
+        }
+        super.setBar(value);
+    }
+
+    /*
+     * Overloaded write accessor for the `bar` slot.
+     * 
+     * This accessor is not strictly necessary, but it makes it clearer that in this
+     * class, the value of the `bar` slot should be a `FirstDerivedBar`. It also
+     * allows to bypass the dynamic check in the normal accessor above, if the
+     * compiler already knows that the assigned value is a FirstDerivedBar.
+     */
+    public void setBar(FirstDerivedBar value) {
+        super.setBar(value);
+    }
+
+    /*
+     * Overridden “Standard” read accessor.
+     * 
+     * We override it to ensure it returns the more specialised subtype.
+     * 
+     * Because the slot could be (and instead is, in this example) refined further
+     * in subclasses, we must still return a generic wildcard, so this accessor has
+     * the same limitation as the one it overrides in the `Foo` class: modifying the
+     * returned list requires an explicit cast into a non-wildcard form.
+     */
+    @Override
+    @SuppressWarnings("unchecked")
+    public List<? extends FirstDerivedBar> getBars() {
+        // This cast should be safe IFF nobody explicitly modify the value returned by
+        // this accessor after casting it into a `List<Bar>`.
+        return (List<FirstDerivedBar>) super.getBars();
+    }
+
+    /*
+     * Overridden read accessor with optional creation of the list.
+     * 
+     * We must override this accessor to ensure that the created list (if the list
+     * needs to be created) is using the more specialised type.
+     */
+    @Override
+    public List<? extends FirstDerivedBar> getBars(boolean create) {
+        // We can delegate the logic to the parent
+        return super.getBars(FirstDerivedBar.class, create);
+    }
+
+    /*
+     * Overridden parameterised read accessor.
+     * 
+     * We must override this accessor to add a runtime check that the given type
+     * parameter is compatible with the more specialised type.
+     */
+    @Override
+    public <T extends Bar> List<T> getBars(Class<T> t) {
+        if ( !FirstDerivedBar.class.isAssignableFrom(t) ) {
+            throw new IllegalArgumentException("Invalid type parameter");
+        }
+        return super.getBars(t);
+    }
+
+    /*
+     * Overridden parameterised read accessor with optional creation of the list.
+     * 
+     * Same as above: we must override this accessor to add a runtime check on the
+     * type parameter.
+     */
+    @Override
+    public <T extends Bar> List<T> getBars(Class<T> t, boolean create) {
+        if ( !FirstDerivedBar.class.isAssignableFrom(t) ) {
+            throw new IllegalArgumentException("Invalid type parameter");
+        }
+        return super.getBars(t, create);
+    }
+
+    /*
+     * Overridden “standard” write accessor.
+     * 
+     * We must override this accessor to include a runtime check. The check must be
+     * performed on all list items.
+     */
+    @Override
+    public void setBars(List<? extends Bar> value) {
+        for ( Bar b : value ) {
+            if ( !(b instanceof FirstDerivedBar) ) {
+                throw new IllegalArgumentException("Invalid bars value");
+            }
+        }
+        super.setBars(value);
+    }
+
+}
diff --git a/core/src/test/java/org/incenp/linkml/core/playground/Foo.java b/core/src/test/java/org/incenp/linkml/core/playground/Foo.java
new file mode 100644
index 0000000..5576616
--- /dev/null
+++ b/core/src/test/java/org/incenp/linkml/core/playground/Foo.java
@@ -0,0 +1,100 @@
+package org.incenp.linkml.core.playground;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * An example of a class whose slots are “refined” in derived classes.
+ */
+public class Foo {
+
+    private Bar bar;
+
+    // We use a wildcard generic to allow derived classes to “refine” the parameter
+    // type
+    private List<? extends Bar> bars;
+
+    /*
+     * Accessors for the `bar` slot.
+     * 
+     * Nothing out of the ordinary here.
+     */
+    public Bar getBar() {
+        return bar;
+    }
+
+    public void setBar(Bar value) {
+        bar = value;
+    }
+
+    /*
+     * Accessors for the multi-valued `bars` slot.
+     */
+
+    /*
+     * “Standard” read accessor. Its return type is parameterized with a wildcard
+     * generic to allow derived classes to refine the parameter.
+     * 
+     * Modifying the returned list is only possible by explicitly casting it to a
+     * non-wildcard form, as in:
+     * 
+     * ((List<Bar>) foo.getBars()).add(new Bar());
+     * 
+     * Without the cast, the following would be a compile-time error:
+     * 
+     * foo.getBars().add(new Bar());
+     */
+    public List<? extends Bar> getBars() {
+        return bars;
+    }
+
+    /*
+     * LinkML-Java “Standard” read accessor with optional creation of the list.
+     * 
+     * This is a convenience accessor, intended to allow client code to dispense
+     * with a null-ness check.
+     * 
+     * As for the argument-less read accessor, the return type is a wildcard, so
+     * modifying the returned list requires an explicit cast.
+     */
+    public List<? extends Bar> getBars(boolean create) {
+        if ( bars == null && create ) {
+            bars = new ArrayList<Bar>();
+        }
+        return bars;
+    }
+
+    /*
+     * Parameterised read accessor.
+     * 
+     * This is another convenience accessor. This one is intended to allow client
+     * code to dispense with an explicit cast to modify the list:
+     * 
+     * foo.getBars(Bar.class).add(new Bar());
+     */
+    @SuppressWarnings("unchecked")
+    public <T extends Bar> List<T> getBars(Class<T> t) {
+        return (List<T>) bars;
+    }
+
+    /*
+     * Parameterised read accessor with optional creation of the list.
+     * 
+     * This is another convenience accessor, combining the effects of the two
+     * accessors above.
+     */
+    @SuppressWarnings("unchecked")
+    public <T extends Bar> List<T> getBars(Class<T> t, boolean create) {
+        if ( bars == null && create ) {
+            bars = new ArrayList<T>();
+        }
+        return (List<T>) bars;
+    }
+
+    /*
+     * “Standard” write accessor.
+     */
+    public void setBars(List<? extends Bar> value) {
+        bars = value;
+    }
+}
diff --git a/core/src/test/java/org/incenp/linkml/core/playground/Playground.java b/core/src/test/java/org/incenp/linkml/core/playground/Playground.java
new file mode 100644
index 0000000..d137b8d
--- /dev/null
+++ b/core/src/test/java/org/incenp/linkml/core/playground/Playground.java
@@ -0,0 +1,115 @@
+package org.incenp.linkml.core.playground;
+
+import java.lang.reflect.Method;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.WildcardType;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class Playground {
+
+    @Test
+    void testFoo() {
+        Foo f = new Foo();
+        f.getBars(Bar.class, true).add(new Bar());
+        // Can add a derived Bar
+        f.getBars(Bar.class).add(new FirstDerivedBar());
+    }
+
+    @Test
+    void testFirstDerivedFoo() {
+        FirstDerivedFoo fdf = new FirstDerivedFoo();
+        try {
+            fdf.getBars(Bar.class, true).add(new Bar());
+            Assertions.fail("Wrong assignment not caught");
+        } catch ( IllegalArgumentException iae ) {
+            Assertions.assertEquals("Invalid type parameter", iae.getMessage());
+        }
+
+        fdf.getBars(FirstDerivedBar.class, true).add(new FirstDerivedBar());
+        // Can access bars items as FirstDerivedBar objects in read mode
+        fdf.getBars().get(0).setLength(9);
+
+        Foo f = fdf;
+        try {
+            // Even when accessed from a Foo object, cannot assign a Bar
+            f.getBars(Bar.class).add(new Bar());
+            Assertions.fail("Wrong assignment not caught");
+        } catch ( IllegalArgumentException iae ) {
+            Assertions.assertEquals("Invalid type parameter", iae.getMessage());
+        }
+    }
+
+    @Test
+    void testSecondDerivedFoo() {
+        SecondDerivedFoo sdf = new SecondDerivedFoo();
+        try {
+            sdf.getBars(Bar.class, true).add(new Bar());
+            Assertions.fail("Wrong assignment not caught");
+        } catch ( IllegalArgumentException iae ) {
+            Assertions.assertEquals("Invalid type parameter", iae.getMessage());
+        }
+
+        sdf.getBars(FirstDerivedBar.class, true).add(new FirstDerivedBar());
+        // Can access bars items as FirstDerivedBar objects in read mode
+        sdf.getBars().get(0).setLength(9);
+
+        FirstDerivedFoo fdf = sdf;
+        try {
+            // Even when accessed from a FirstDerivedFoo object, cannot assign a Bar
+            fdf.getBars(Bar.class).add(new Bar());
+            Assertions.fail("Wrong assignment not caught");
+        } catch ( IllegalArgumentException iae ) {
+            Assertions.assertEquals("Invalid type parameter", iae.getMessage());
+        }
+
+        Foo f = sdf;
+        try {
+            // Even when accessed from a Foo object, cannot assign a Bar
+            f.getBars(Bar.class).add(new Bar());
+            Assertions.fail("Wrong assignment not caught");
+        } catch ( IllegalArgumentException iae ) {
+            Assertions.assertEquals("Invalid type parameter", iae.getMessage());
+        }
+    }
+
+    @Test
+    void testThirdDerivedFoo() {
+        ThirdDerivedFoo tdf = new ThirdDerivedFoo();
+        try {
+            tdf.getBars(FirstDerivedBar.class, true).add(new FirstDerivedBar());
+            Assertions.fail("Wrong assignment not caught");
+        } catch ( IllegalArgumentException iae ) {
+            Assertions.assertEquals("Invalid type parameter", iae.getMessage());
+        }
+
+        tdf.getBars(SecondDerivedBar.class, true).add(new SecondDerivedBar());
+        // Can access bars items as FirstDerivedBar objects in read mode
+        tdf.getBars().get(0).setLength(9);
+
+        Foo f = tdf;
+        try {
+            // Even when accessed from a Foo object, cannot assign a Bar
+            f.getBars(Bar.class).add(new Bar());
+            Assertions.fail("Wrong assignment not caught");
+        } catch ( IllegalArgumentException iae ) {
+            Assertions.assertEquals("Invalid type parameter", iae.getMessage());
+        }
+    }
+
+    @Test
+    void testObtainingParameterBound() {
+        Class<?> klass = FirstDerivedFoo.class;
+        Method m = null;
+        try {
+            m = klass.getDeclaredMethod("getBars", (Class<?>[]) null);
+        } catch ( NoSuchMethodException | SecurityException e ) {
+            Assertions.fail("No getBars method");
+        }
+
+        ParameterizedType t = (ParameterizedType) m.getGenericReturnType();
+        WildcardType t2 = (WildcardType) t.getActualTypeArguments()[0];
+        Assertions.assertEquals(FirstDerivedBar.class, t2.getUpperBounds()[0]);
+    }
+}
diff --git a/core/src/test/java/org/incenp/linkml/core/playground/SecondDerivedBar.java b/core/src/test/java/org/incenp/linkml/core/playground/SecondDerivedBar.java
new file mode 100644
index 0000000..b13c9a4
--- /dev/null
+++ b/core/src/test/java/org/incenp/linkml/core/playground/SecondDerivedBar.java
@@ -0,0 +1,11 @@
+package org.incenp.linkml.core.playground;
+
+/**
+ * Second derived class from Bar.
+ * <p>
+ * This class is used, instead of its parent <code>FirstDerivedBar</code>, in
+ * {@link ThirdDerivedFoo}.
+ */
+public class SecondDerivedBar extends FirstDerivedBar {
+
+}
diff --git a/core/src/test/java/org/incenp/linkml/core/playground/SecondDerivedFoo.java b/core/src/test/java/org/incenp/linkml/core/playground/SecondDerivedFoo.java
new file mode 100644
index 0000000..763a144
--- /dev/null
+++ b/core/src/test/java/org/incenp/linkml/core/playground/SecondDerivedFoo.java
@@ -0,0 +1,13 @@
+package org.incenp.linkml.core.playground;
+
+/**
+ * An example of a class that inherits from a class that refines its slots, but
+ * that does no do any refinement itself.
+ */
+public class SecondDerivedFoo extends FirstDerivedFoo {
+
+    /*
+     * In this class, the `bar` and `bars` slot are of the same type as in the
+     * parental `FirstDerivedFoo` class, so no overriding of accessors is necessary.
+     */
+}
diff --git a/core/src/test/java/org/incenp/linkml/core/playground/ThirdDerivedFoo.java b/core/src/test/java/org/incenp/linkml/core/playground/ThirdDerivedFoo.java
new file mode 100644
index 0000000..9ab295c
--- /dev/null
+++ b/core/src/test/java/org/incenp/linkml/core/playground/ThirdDerivedFoo.java
@@ -0,0 +1,139 @@
+package org.incenp.linkml.core.playground;
+
+import java.util.List;
+
+/**
+ * An example of a class that refines the range of its slots, that it inherited
+ * from a class that already refined them.
+ * 
+ * Importantly, this class has no derived class, so we know its slots cannot be
+ * further refined by another class.
+ */
+public class ThirdDerivedFoo extends SecondDerivedFoo {
+
+    /*
+     * Overridden read accessor for the `bar` slot.
+     * 
+     * We override it to ensure that it returns the more specialised subtype.
+     */
+    @Override
+    public SecondDerivedBar getBar() {
+        return (SecondDerivedBar) super.getBar();
+    }
+
+    /*
+     * Overridden write accessor for the `bar` slot.
+     * 
+     * We override it to add a runtime check to enforce the more specialised type
+     * constraint. We cannot prevent client code from trying to assign an object of
+     * the wrong type, but if that happens we can at least immediately throw an
+     * exception.
+     */
+    @Override
+    public void setBar(Bar value) {
+        if ( !(value instanceof SecondDerivedBar) ) {
+            throw new IllegalArgumentException("Invalid bar value");
+        }
+        super.setBar(value);
+    }
+
+    /*
+     * Second overridden write accessor for the `bar` slot.
+     * 
+     * Since `FirstDerivedFoo` defined this accessor, we must override it as well,
+     * otherwise it would allow client code to assign a FirstDerivedBar to the slot.
+     */
+    @Override
+    public void setBar(FirstDerivedBar value) {
+        if ( !(value instanceof SecondDerivedBar) ) {
+            throw new IllegalArgumentException("Invalid bar value");
+        }
+        super.setBar(value);
+    }
+
+    /*
+     * Overloaded write accessor for the `bar` slot.
+     * 
+     * This accessor is not strictly necessary, but it makes it clearer that in this
+     * class, the value of the `bar` slot should be a `SecondDerivedBar`. It also
+     * allows to bypass the dynamic check in the normal accessor above, if the
+     * compiler already knows that the assigned value is a FirstDerivedBar.
+     */
+    public void setBar(SecondDerivedBar value) {
+        super.setBar(value);
+    }
+
+    /*
+     * Overridden “standard” read accessor.
+     * 
+     * We override it to ensure it returns the more specialised subtype.
+     * 
+     * Here, since we know the slot cannot be further refined (no subclass), we can
+     * dispense with a wildcard generic.
+     */
+    @Override
+    @SuppressWarnings("unchecked")
+    public List<SecondDerivedBar> getBars() {
+        return (List<SecondDerivedBar>) super.getBars();
+    }
+
+    /*
+     * Overriden read accessor with optional creation of the list.
+     * 
+     * We must override this accessor to ensure that the created list (if the list
+     * needs to be created) is using the more specialised type.
+     */
+    @Override
+    public List<SecondDerivedBar> getBars(boolean create) {
+        // We can delegate the logic to the parent
+        return super.getBars(SecondDerivedBar.class, create);
+    }
+
+    /*
+     * Overidden parameterised read accessor.
+     * 
+     * In this class, we don’t need this accessor to get a modifiable list (we can
+     * use `getBars()` directly), but we must still override the accessor we inherit
+     * from the parent, otherwise this would allow client code to get a
+     * `List<FirstDerivedBar>`-typed value.
+     */
+    @Override
+    public <T extends Bar> List<T> getBars(Class<T> t) {
+        if ( !SecondDerivedBar.class.isAssignableFrom(t) ) {
+            throw new IllegalArgumentException("Invalid type parameter");
+        }
+        return super.getBars(t);
+    }
+
+    /*
+     * Overridden parameterised read accessor with optional creation of the list.
+     * 
+     * Same as above: we must override this accessor to add a runtime check on the
+     * type parameter.
+     */
+    @Override
+    public <T extends Bar> List<T> getBars(Class<T> t, boolean create) {
+        if ( !SecondDerivedBar.class.isAssignableFrom(t) ) {
+            throw new IllegalArgumentException("Invalid type parameter");
+        }
+        return super.getBars(t, create);
+    }
+
+    /*
+     * Overridden “standard” write accessor.
+     * 
+     * We must override this accessor to include a runtime check. The check must be
+     * performed on all list items.
+     */
+    @Override
+    public void setBars(List<? extends Bar> value) {
+        for ( Bar b : value ) {
+            if ( !(b instanceof SecondDerivedBar) ) {
+                throw new IllegalArgumentException("Invalid bar value");
+            }
+        }
+        // FIXME: the parent method will in turn perform a (no longer needed) runtime
+        // check...
+        super.setBars(value);
+    }
+}