Here is an example that illustrates my question.

• I have a program that lists 1000 items.
• I select 10 of 1000 items.
• The program enables a button indicating that a command is available for my selection.
• I click the button, and a window appears.
• I make some change in the window and click OK.
• The command changes 5 of the 10 items in my multiple selection, and those 5 changed items now reflect a modified state in my list.

My question is:

How do I indicate to user that the command affects a subset of a multiple selection before clicking OK?

Can anyone cite examples of existing products that handle this scenario well?