[R] package precedence question

[stephen at mnemosyne.co.uk]

Dear R help

I am writing a package where I am intending to extend the png function of the grDevices package. When I load my package, my png function indeed substitutes the grDevices function, and everything seems OK. I am a little confused though at how function precedence is determined. I am concerned that when the package moves into production on a webserver that instances may occur when the precedence breaks and the grDevices function becomes the version. I wish to avoid the need for the explicit calling of the myPackage:::png function, is there a way to encourage or coerce the precedence with which packages are loaded and in which functions are evaluated.

Some pointers as to where I might find the solution (or a more appropriate nomenclature) would be very gratefully received.

Thanks

Stephen