https://learn.microsoft.com/ja-jp/dotnet/api/system.attributeusageattribute.allowmultiple?view=netframework-4.8.1&viewFallbackFrom=net-10.0
AttributeUsageAttribute.AllowMultiple Property (System) | Microsoft Learn
Gets or sets a Boolean value indicating whether more than one instance of the indicated attribute can be specified for a single program element.
property systemmicrosoftlearn
https://dotnetframework.org/default.aspx/DotNET/DotNET/8@0/untmp/whidbey/REDBITS/ndp/clr/src/BCL/System/AttributeUsageAttribute@cs/1/AttributeUsageAttribute@cs
AttributeUsageAttribute.cs source code in C# .NET
cs sourcecode