What is the difference between d:Source and d:DesignSource?

Question

There are two design-time attributes - d:Source and d:DesignSource. It seems both could be used for design data specification for CollectionViewSource:

<CollectionViewSource x:Key="GrouppedCollection"
                      IsSourceGrouped="true"
                      Source="{Binding GroupedItems}"
                      d:Source="{Binding GroupedItems,
                                         Source={d:DesignInstance
                                                   Type=vm:MyViewModel,
                                                   IsDesignTimeCreatable=True}}" />

OR

<CollectionViewSource x:Key="GrouppedCollection"
                      IsSourceGrouped="true"
                      Source="{Binding GroupedItems}"
                      d:DesignSource="{Binding GroupedItems,
                                               Source={d:DesignInstance
                                                         Type=vm:MyViewModel,
                                                         IsDesignTimeCreatable=True}}" />

Is there any difference between them or they are just two names for the same thing?