code: func IPMaskVar(p *net.IPMask, name string, value net.IPMask, usage string) {
  	CommandLine.VarP(newIPMaskValue(value, p), name, "", usage)
  }
docs: // IPMaskVar defines an net.IPMask flag with specified name, default value, and usage string.
  // The argument p points to an net.IPMask variable in which to store the value of the flag.