Unified detail views, model

CHDataManagement/Model/Page.swift

@@ -66,9 +66,16 @@ final class Page: Item {
         super.init(content: content, id: id)
     }
 
+    func isValid(id: String) -> Bool {
+        !id.isEmpty &&
+        content.isValidIdForTagOrPageOrPost(id) &&
+        content.isNewIdForPage(id)
+    }
+
+    @discardableResult
     func update(id newId: String) -> Bool {
         guard content.storage.move(page: id, to: newId) else {
-            print("Failed to move file of page \(id)")
+            print("Failed to move files of page \(id)")
             return false
         }
         id = newId