R Leaflet custom attribution string

Question

When using the R leaflet package, how can I add something additional to the attribution string (i.e. the "Leaflet | ..." in the bottom right corner)?

For example, I how would I add something like "data source: ..." to the attribution text on this map:

leaflet(data = quakes[1:20,]) %>% 
  addTiles() %>%
  addMarkers(~long, ~lat, popup = ~as.character(mag), label = ~as.character(mag))

Answer 1

As @rensa suspects, their second option does indeed embed and fetch both tile sets. However, the setting a blank urlTemplate seems to stop it:

leaflet(data = quakes[1:20,]) %>% 
  addProviderTiles(providers$OpenStreetMap.Mapnik) %>%
  addTiles(urlTemplate = "", attribution = 'I did this, you hear?! Also Leaflet.')