diff --git a/slhx-build/src/lib.rs b/slhx-build/src/lib.rs
index b19a664..94dc7ed 100644
--- a/slhx-build/src/lib.rs
+++ b/slhx-build/src/lib.rs
@@ -149,6 +149,8 @@ impl Resources {
                 continue;
             };
 
+            reject_selector_target_attrs(path, &node.attrs)?;
+
             if let Some(class_attr) = static_attr(&node.attrs, "class") {
                 for token in class_tokens(&class_attr) {
                     let canonical = canonical_symbol(root, path, token);
@@ -950,6 +952,22 @@ fn is_inside_keyed_for(surface: &SurfaceDocument, mut scope: ScopeId) -> bool {
     }
 }
 
+fn reject_selector_target_attrs(path: &Path, attrs: &[SurfaceAttribute]) -> io::Result<()> {
+    for attr in attrs {
+        let name = attr.name.as_str();
+        if matches!(name, "data-slhx-target" | "data-slhx-select") {
+            return Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                format!(
+                    "{}: `{name}` is selector-style targeting; slhx uses generated resources instead. Add data-slhx-slot to the local element and return an effect for that generated slot.",
+                    path.display()
+                ),
+            ));
+        }
+    }
+    Ok(())
+}
+
 fn reject_unkeyed_loop(
     surface: &SurfaceDocument,
     mut scope: ScopeId,
@@ -1345,6 +1363,37 @@ fn main() {{
         }
     }
 
+    #[test]
+    fn rejects_selector_style_targeting_attrs() {
+        // req: locality/001 req: locality/002 req: htmx_equivalents/003
+        for (case, template, attr) in [
+            (
+                "slhx-target",
+                r##"<button data-slhx-handle="save" data-slhx-target="#row">Save</button>"##,
+                "data-slhx-target",
+            ),
+            (
+                "slhx-select",
+                r##"<button data-slhx-handle="save" data-slhx-select="closest tr">Save</button>"##,
+                "data-slhx-select",
+            ),
+        ] {
+            let base = test_dir(&format!("slhx-build-selector-target-{case}-test"));
+            let templates = base.join("templates");
+            let out = base.join("out");
+            let _ = std::fs::remove_dir_all(&base);
+            std::fs::create_dir_all(&templates).unwrap();
+            std::fs::write(templates.join("target.heml"), template).unwrap();
+
+            let err = app().template_dir(&templates).out_dir(&out).run().unwrap_err();
+            assert!(err.to_string().contains(attr), "missing attr in diagnostic: {err}");
+            assert!(err.to_string().contains("selector-style targeting"), "missing selector diagnostic: {err}");
+            assert!(err.to_string().contains("data-slhx-slot"), "missing suggested slot fix: {err}");
+
+            let _ = std::fs::remove_dir_all(&base);
+        }
+    }
+
     #[test]
     fn generated_lowering_injects_progressive_form_handle_and_key() {
         // req: form/002, req: wire/001