TREX URL-based search with properties

Hi,

I would like to use TREX search using an URL-based query.  I would like to use custom Metadata (properties) and a search query. 

I have discovered that the use of the URL parameter "SearchTerm", a search term can be passed to the TREX Search IView. 

I have found the URL parameter "SelectedCustomProps" but I don't know how to use it.  Does someone have the correct syntax?

Thanks.

Dick