Ability to add query string. 

Added ability to append {$filter} to the url. {$filter} being the query string of the page the button is on.

I chose {$filter} because you used {$root} for the prepend. (personally i think using the $ makes it look too much like parameters which they clearly are not ;-) )

Use case:

When you are on a page that is filtered (?filter=[field]:[value]) and you want to pass this filter to another extension (for example: to export a .csv) this enables you to do just that.