diff --git a/source/fluid/code_input.d b/source/fluid/code_input.d
index 09653c6..72ecd77 100644
--- a/source/fluid/code_input.d
+++ b/source/fluid/code_input.d
@@ -2065,9 +2065,9 @@ unittest {
             else
                 return 1;
 
-        };
+        }
 
-    };
+    }
 
     // Every new line indents. If "end" is found in the text, every new line *outdents*, effectively making the text
     // flat.
diff --git a/source/fluid/input.d b/source/fluid/input.d
index 7eab4c1..3afc31f 100644
--- a/source/fluid/input.d
+++ b/source/fluid/input.d
@@ -764,18 +764,24 @@ interface FluidHoverable {
     /// Returns:
     ///     * `true` if the handler took care of the action; processing of the action will finish.
     ///     * `false` if the action should be handled by the default input action handler.
-    bool inputActionImpl(InputActionID id, bool active);
+    bool inputActionImpl(immutable InputActionID id, bool active);
 
     /// Run input actions.
     ///
     /// Use `mixin enableInputActions` to implement.
     ///
     /// Manual implementation is discouraged; override `inputActionImpl` instead.
-    bool runInputAction(InputActionID action, bool active = true);
+    bool runInputActionImpl(immutable InputActionID action, bool active = true);
+
+    final bool runInputAction(immutable InputActionID action, bool active = true) {
+
+        return runInputActionImpl(action, active);
+
+    }
 
     final bool runInputAction(alias action)(bool active = true) {
 
-        return runInputAction(InputActionID.from!action, active);
+        return runInputActionImpl(InputActionID.from!action, active);
 
     }
 
@@ -814,22 +820,15 @@ interface FluidHoverable {
         static assert(is(typeof(this) : Node),
             format!"%s : FluidHoverable must inherit from Node"(typeid(this)));
 
-        // For some reason, a simple alias to FluidHoverable.runInputAction doesn't work
-        final bool runInputAction(alias action)(bool active = true) {
-
-            return runInputAction(InputActionID.from!action, active);
-
-        }
-
         // Provide a default implementation of inputActionImpl
         static if (!is(typeof(super) : FluidHoverable))
-        bool inputActionImpl(InputActionID id, bool active) {
+        bool inputActionImpl(immutable InputActionID id, bool active) {
 
             return false;
 
         }
 
-        override bool runInputAction(InputActionID action, bool active = true) {
+        override bool runInputActionImpl(immutable InputActionID action, bool active) {
 
             import std.meta : Filter;
 
diff --git a/source/fluid/map_frame.d b/source/fluid/map_frame.d
index 7c2f6b8..def2304 100644
--- a/source/fluid/map_frame.d
+++ b/source/fluid/map_frame.d
@@ -496,7 +496,7 @@ class MapFrame : Frame {
         const position = MapPosition(rectangle.start);
 
         // Already a child
-        if (children.canFind(node)) {
+        if (children.canFind!"a is b"(node)) {
 
             positions[node] = position;
 
diff --git a/source/fluid/node.d b/source/fluid/node.d
index f47b4ee..b3e1f0c 100644
--- a/source/fluid/node.d
+++ b/source/fluid/node.d
@@ -230,6 +230,12 @@ abstract class Node {
     /// Direct changes are discouraged, and are likely to be discarded when reloading themes. Use themes instead.
     ref inout(Style) style() inout { return _style; }
 
+    override bool opEquals(Object other) const {
+
+        return this is other;
+
+    }
+
     bool opEquals(const Node otherNode) const {
 
         return this is otherNode;
@@ -538,7 +544,7 @@ abstract class Node {
 
         root.draw();
 
-        assert(visitedNodes == allNodes[1..3]);
+        assert(visitedNodes[] == allNodes[1..3]);
 
     }
 
diff --git a/source/fluid/structs.d b/source/fluid/structs.d
index 18758a2..deb205b 100644
--- a/source/fluid/structs.d
+++ b/source/fluid/structs.d
@@ -183,7 +183,7 @@ struct Layout {
 /// Tags are optional "marks" left on nodes that are used to apply matching styles. Tags closely resemble
 /// [HTML classes](https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/class).
 ///
-/// Tags have to be explicitly defined before usage, by creating an enum and marking it with the `@NodeTag` attribute.
+/// Tags have to be explicitly defined before usage by creating an enum and marking it with the `@NodeTag` attribute.
 /// Such tags can then be applied by passing them to the constructor.
 enum NodeTag;
 
@@ -197,6 +197,8 @@ unittest {
         myTag,
     }
 
+    static assert(isNodeTag!(Tags.myTag));
+
     auto myLabel = label(
         .tags!(Tags.myTag),
         "Hello, World!"
@@ -207,16 +209,34 @@ unittest {
 }
 
 /// Check if the given item is a node tag.
-enum isNodeTag(alias tag)
+template isNodeTag(alias tag) {
+
     // @NodeTag enum Tag;
     // enum Tag { @NodeTag tag }
-    = (isSomeEnum!tag
-      && hasUDA!(tag, NodeTag)) 
+    enum isDirectTag
+        = isSomeEnum!tag
+        && hasUDA!(tag, NodeTag);
+
+    // Get the parent symbol
+    alias parent = __traits(parent, tag);
 
     // @NodeTag enum Enum { tag }
-    || (!isType!tag 
-        && is(__traits(parent, tag) == enum)
-        && hasUDA!(typeof(tag), NodeTag));
+    enum isTagMember
+        = !isType!tag 
+        && is(parent == enum)
+        && hasUDA!(typeof(tag), NodeTag);
+
+    pragma(msg, tag, " ", isDirectTag, " ", isTagMember);
+    pragma(msg, "  isDirectTag: ", isSomeEnum!tag, 
+        ", ", hasUDA!(tag, NodeTag));
+    pragma(msg, "  parent: ", parent);
+    pragma(msg, "  isTagMember: ", !isType!tag,
+        ", ", is(__traits(parent, tag) == enum),
+        ", ", hasUDA!(typeof(tag), NodeTag));
+
+    enum isNodeTag = isDirectTag || isTagMember;
+
+}
 
 /// Test if the given symbol is an enum, or an enum member. 
 enum isSomeEnum(alias tag) 
diff --git a/source/fluid/theme.d b/source/fluid/theme.d
index 0133448..de41d83 100644
--- a/source/fluid/theme.d
+++ b/source/fluid/theme.d
@@ -10,6 +10,7 @@ import std.traits;
 import std.exception;
 
 import fluid.node;
+import fluid.utils;
 import fluid.style;
 import fluid.backend;
 import fluid.structs;
@@ -1535,9 +1536,9 @@ private struct FieldValueStaticArray(E, size_t n) {
         isSet = true;
 
         // Assign each field
-        foreach (i, ref field; this.value.tupleof) {
+        foreach (i, ref field; this.value[]) {
 
-            field = value.tupleof[i];
+            field = value[i];
 
         }
 
@@ -1599,8 +1600,8 @@ private struct FieldValueStaticArray(E, size_t n) {
 
         if (!isSet) return;
 
-        foreach (i, field; this.value.tupleof) {
-            field.apply(value.tupleof[i]);
+        foreach (i, field; this.value[]) {
+            field.apply(value[i]);
         }
 
     }
@@ -1612,7 +1613,7 @@ private struct FieldValueStaticArray(E, size_t n) {
 
         value.isSet = true;
 
-        foreach (i, field; this.value.tupleof) {
+        foreach (i, field; this.value[]) {
             field.apply(value.value[i]);
         }