The package provides macros \DeclareRobustActChar and \ReDeclareRobActChar. One uses \DeclareRobustActChar in the same way one would use \DeclareRobustCommand; the macro \protects the active character when it appears in a moving argument. \ReDeclareRobActChar redefines an active character previously defined with \DeclareRobustActChar, in the same way that \renewcommand works for ordinary commands.