Enable And / Or On Custom Search Form

I've created a custom search form where using unbound text boxes and combo boxes I enter the criteria for a query. I would like to enhance my form to allow "and" and "or" searches on a field. For example, a product on my database has multiple features. I would like to search for products who have "feature1 and feature 2" or "feature1 or feature2". {Note: The table, Product is connected to table, Features using table, LineItem_ProdFeature where there are multiple records in Features for one record in Product}

Right now, the search form has a combo box that lists all product features. The user selects a feature and runs the query. All products with that feature are listed in the query.

It would be so great if the user could choose multiple features from the combo box. Then the query would return all products that have all of the selected features ("and" search). It would be just awesome if the user could select multiple features, and specify if they want an "and" or "or" search of those features.