Search results from multiple collections (paramater syntax)

I have a template where I want to restrict search results to specific collections, and just trying to get the syntax right. Here's what I have so far:

{{ search:results collection:is="collection-1|collection-2|collection-3" }}

However, this clearly isn't right as doesn't return any results, unless I just list one collection. Can anyone tell me the correct syntax?

Answered by Jack McDade!
>>>>>>> Answered <<<<<<<
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