Pre-fill forms on Zoho forms?

Pre-fill forms on Zoho forms?

Seems like this would be something easily found on the forums, but I'm not easily finding documentation on this.  But, how can I pre-form fields for an embedded form? IE - they click a button - I want to know what button and where they clicked from.  If they're logged in - what's their name, etc?

Can this be passed by url parameters or how?