change to union multiple from, not combine them as sub-fields

demo/advanced.yaml

@@ -32,6 +32,12 @@ fields:
     prefix: "["
     postfix: "]\t"
 
+  - field: field_union_instant
+    from: jenkins.ip.private.yaml       # 內置instances使用了多个use-from。
+    use: privateB_union_privateC
+    prefix: "["
+    postfix: "]\t"
+
   - field: field_from_muti
     prefix: "["
     postfix: "]\t"

users/jenkins/ip/private.yaml

@@ -15,6 +15,23 @@ instances:
         prefix: ""
         postfix: "/"
 
+      - field: part2
+        from: jenkins.number.v1.yaml
+        use: netmask
+
+  - instance: privateB_union_privateC
+    note: 使用多个use-from引用原始IP地址定义
+
+    fields:
+      - field: part1
+        froms:
+          - from: ip.v1.yaml
+            use: privateB{2}
+          - from: ip.v1.yaml
+            use: privateC{3}
+        prefix: ""
+        postfix: "/"
+
       - field: part2
         from: jenkins.number.v1.yaml
         use: netmask
\ No newline at end of file