diff --git a/.mxcli/widgets/gallery.def.json b/.mxcli/widgets/gallery.def.json
index 2510aa9..d300c58 100644
--- a/.mxcli/widgets/gallery.def.json
+++ b/.mxcli/widgets/gallery.def.json
@@ -17,7 +17,8 @@
     {
       "propertyKey": "itemSelection",
       "source": "Selection",
-      "operation": "selection"
+      "operation": "selection",
+      "default": "Single"
     },
     {
       "propertyKey": "itemSelectionMode",
@@ -78,7 +79,7 @@
     },
     {
       "propertyKey": "filtersPlaceholder",
-      "mdlContainer": "FILTERSPLACEHOLDER",
+      "mdlContainer": "FILTER",
       "operation": "widgets"
     }
   ]
diff --git a/cmd/mxcli/cmd_widget.go b/cmd/mxcli/cmd_widget.go
index a6f4fe1..4ec508a 100644
--- a/cmd/mxcli/cmd_widget.go
+++ b/cmd/mxcli/cmd_widget.go
@@ -5,6 +5,7 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"log"
 	"os"
 	"path/filepath"
 	"strings"
@@ -195,7 +196,9 @@ func runWidgetList(cmd *cobra.Command, args []string) error {
 	// Load user definitions if project path available
 	projectPath, _ := cmd.Flags().GetString("project")
 	if projectPath != "" {
-		_ = registry.LoadUserDefinitions(projectPath)
+		if err := registry.LoadUserDefinitions(projectPath); err != nil {
+			log.Printf("warning: loading user widget definitions: %v", err)
+		}
 	}
 
 	defs := registry.All()
diff --git a/cmd/mxcli/lsp_completion.go b/cmd/mxcli/lsp_completion.go
index 95d1e09..7fa3a5f 100644
--- a/cmd/mxcli/lsp_completion.go
+++ b/cmd/mxcli/lsp_completion.go
@@ -4,6 +4,7 @@ package main
 
 import (
 	"context"
+	"log"
 	"strings"
 
 	"github.com/mendixlabs/mxcli/mdl/executor"
@@ -89,8 +90,7 @@ func (s *mdlServer) widgetRegistryCompletions() []protocol.CompletionItem {
 			return
 		}
 		if err := registry.LoadUserDefinitions(s.mprPath); err != nil {
-			// Non-fatal: user definitions are optional
-			_ = err
+			log.Printf("warning: loading user widget definitions for LSP: %v", err)
 		}
 		for _, def := range registry.All() {
 			s.widgetCompletionItems = append(s.widgetCompletionItems, protocol.CompletionItem{
diff --git a/docs-site/book.toml b/docs-site/book.toml
index 4aa87a6..6beb6a2 100644
--- a/docs-site/book.toml
+++ b/docs-site/book.toml
@@ -15,6 +15,7 @@ git-repository-url = "https://github.com/mendixlabs/mxcli"
 edit-url-template = "https://github.com/mendixlabs/mxcli/edit/main/docs-site/src/{path}"
 site-url = "/mxcli/"
 additional-css = ["theme/custom.css"]
+additional-js = ["theme/mermaid-init.js"]
 
 [output.html.search]
 enable = true
diff --git a/docs-site/theme/mermaid-init.js b/docs-site/theme/mermaid-init.js
new file mode 100644
index 0000000..a38cec4
--- /dev/null
+++ b/docs-site/theme/mermaid-init.js
@@ -0,0 +1,24 @@
+// Render mermaid diagrams in mdbook.
+// mdbook renders ```mermaid blocks as <code class="language-mermaid"> inside <pre>.
+// This script loads mermaid from CDN and converts them to rendered SVG diagrams.
+(function () {
+  var blocks = document.querySelectorAll('code.language-mermaid');
+  if (blocks.length === 0) return;
+
+  var script = document.createElement('script');
+  script.src = 'https://cdn.jsdelivr.net/npm/mermaid@11/dist/mermaid.min.js';
+  script.onload = function () {
+    mermaid.initialize({ startOnLoad: false, theme: 'default' });
+
+    blocks.forEach(function (code, i) {
+      var pre = code.parentElement;
+      var container = document.createElement('div');
+      container.className = 'mermaid';
+      container.textContent = code.textContent;
+      pre.parentElement.replaceChild(container, pre);
+    });
+
+    mermaid.run();
+  };
+  document.head.appendChild(script);
+})();
diff --git a/docs/plans/2026-03-25-pluggable-widget-engine-design.md b/docs/plans/2026-03-25-pluggable-widget-engine-design.md
index 4b4a712..9a10ade 100644
--- a/docs/plans/2026-03-25-pluggable-widget-engine-design.md
+++ b/docs/plans/2026-03-25-pluggable-widget-engine-design.md
@@ -1,23 +1,23 @@
-# Pluggable Widget Engine: 声明式 Widget 构建系统
+# Pluggable Widget Engine: Declarative Widget Build System
 
 **Date**: 2026-03-25
 **Status**: Implemented
 
 ## Problem
 
-当前每个 pluggable widget 都需要硬编码一个 Go builder 函数（`buildComboBoxV3`, `buildGalleryV3` 等），加上 switch case 注册。新增一个 widget 需要改 4 个地方：
+Each pluggable widget currently requires a hardcoded Go builder function (`buildComboBoxV3`, `buildGalleryV3`, etc.) plus a switch-case registration. Adding a new widget requires changes in 4 places:
 
-1. `sdk/pages/pages_widgets_advanced.go` — 添加 WidgetID 常量
-2. `sdk/widgets/templates/` — 添加 JSON 模板
-3. `mdl/executor/cmd_pages_builder_v3_pluggable.go` — 写专属 build 函数（50-200 行）
-4. `mdl/executor/cmd_pages_builder_v3.go` — 在 `buildWidgetV3()` switch 中添加 case
+1. `sdk/pages/pages_widgets_advanced.go` — Add WidgetID constant
+2. `sdk/widgets/templates/` — Add JSON template
+3. `mdl/executor/cmd_pages_builder_v3_pluggable.go` — Write a dedicated build function (50-200 lines)
+4. `mdl/executor/cmd_pages_builder_v3.go` — Add case in `buildWidgetV3()` switch
 
-这导致：
-- 用户无法自行添加 pluggable widget 支持
-- 大量重复代码（30+ builder 函数共享 ~80% 骨架）
-- 维护成本随 widget 数量线性增长
+This causes:
+- Users cannot add pluggable widget support on their own
+- Significant code duplication (30+ builder functions sharing ~80% boilerplate)
+- Maintenance cost grows linearly with widget count
 
-## Solution: 声明式 Widget 定义 + 通用构建引擎
+## Solution: Declarative Widget Definitions + Generic Build Engine
 
 ### Architecture
 
@@ -126,7 +126,7 @@ Gallery (with child slots):
   "childSlots": [
     {"propertyKey": "content", "mdlContainer": "TEMPLATE", "operation": "widgets"},
     {"propertyKey": "emptyPlaceholder", "mdlContainer": "EMPTYPLACEHOLDER", "operation": "widgets"},
-    {"propertyKey": "filtersPlaceholder", "mdlContainer": "FILTERSPLACEHOLDER", "operation": "widgets"}
+    {"propertyKey": "filtersPlaceholder", "mdlContainer": "FILTER", "operation": "widgets"}
   ]
 }
 ```