This option allows you to see the data for an entity record in a slightly more user-friendly view.
Here is a RIMMF record–
–displayed in OPAC view:
The OPAC view opens in RIMMF's built-in browser–so if you have anything else this window, e.g., the RDA Toolkit (because of a link to an RDA rule), then the toolkit window will be replaced with the opac view. You can use the 'Prev' and 'Next' buttons in the browser window to get back to the Toolkit window.