<PackageReference Include="System.Security.Permissions" Version="10.0.4" />

System.Security.Policy.FirstMatchCodeGroup

public sealed class FirstMatchCodeGroup : CodeGroup
Allows security policy to be defined by the union of the policy statement of a code group and that of the first child code group that matches. This class cannot be inherited.
namespace System.Security.Policy { public sealed class FirstMatchCodeGroup : CodeGroup { public FirstMatchCodeGroup(IMembershipCondition membershipCondition, PolicyStatement policy); } }