[Rd] generic '[' for a non-exported class

[Christophe Genolini]

Hi all,
I define a S4 class 'foo'. I define '[' and '[<-' for it.
I do not want to export foo, so I do not put it in NAMESPACE.
I do not want to export '[' and '[<-' either (since the user can not use 
foo, no raison to give him access to '[' for foo).

But R CMD check does not agree with me and report an error:
Undocumented S4 methods:
  generic '[' and siglist 'foo'
  generic '[<-' and siglist 'foo'


Any solution ?
Christophe