[FIX] some missing doc

uml4net/Decorators/ReferencedPropertyAttribute.cs

@@ -48,14 +48,29 @@ public ReferencedPropertyAttribute(string propertyName)
         {
             this.PropertyName = propertyName;
         }
-
+        /// <summary>
+        /// Retrieves the property name from the <see cref="ReferencedPropertyAttribute"/> of the specified <see cref="IReferenceable{T}"/> instance.
+        /// </summary>
+        /// <typeparam name="T">The type parameter of the referenced element.</typeparam>
+        /// <param name="instance">The instance of the <see cref="IReferenceable{T}"/> interface from which the property name is retrieved.</param>
+        /// <returns>The name of the referenced property specified in the <see cref="ReferencedPropertyAttribute"/>.</returns>
+        /// <exception cref="InvalidOperationException">Thrown if the referenced property cannot be found.</exception>
         public static string GetName<T>(IReferenceable<T> instance)
         {
             var memberInfo = GetExplicitInterfaceProperty(instance);
             var customAttribute = Attribute.GetCustomAttribute(memberInfo, typeof(ReferencedPropertyAttribute));
             return ((ReferencedPropertyAttribute)customAttribute).PropertyName;
         }
-
+
+        /// <summary>
+        /// Retrieves the <see cref="PropertyInfo"/> of the explicit interface implementation for the <see cref="IReferenceable{T}.Reference"/> property.
+        /// </summary>
+        /// <typeparam name="T">The type parameter of the referenced element.</typeparam>
+        /// <param name="instance">The instance of the <see cref="IReferenceable{T}"/> interface to inspect.</param>
+        /// <returns>
+        /// The <see cref="PropertyInfo"/> of the <see cref="IReferenceable{T}.Reference"/> property.
+        /// </returns>
+        /// <exception cref="InvalidOperationException">Thrown if the explicit interface implementation of the Reference property is not found.</exception>
         public static PropertyInfo GetExplicitInterfaceProperty<T>(IReferenceable<T> instance)
         {
             var instanceType = instance.GetType();

uml4net/POCO/Values/StringExpression.cs

@@ -77,6 +77,13 @@ public class StringExpression : XmiElement, IStringExpression, IReferenceable<IS
         [Implements(implementation: "INamedElement.NameExpression")]
         public IStringExpression NameExpression { get; set; }
 
+        /// <summary>
+        /// Gets or sets the reference to the NameExpression owned by this element.
+        /// </summary>
+        /// <remarks>
+        /// This property implements the <see cref="IReferenceable{T}"/> interface,
+        /// providing access to the owned comments through the <see cref="NameExpression"/> property.
+        /// </remarks>
         IStringExpression IReferenceable<IStringExpression>.Reference
         {
             get => this.NameExpression;