Question re lax crossed modules

I have been looking at categorical groups a little and was wondering what a lax crossed module is. A search through various databases has turned up nothing. It would seem that they should be like crossed modules but only satisfy a weakened equivariance property. Any pointers toward a definition would be great. ------------------------------------------------------------------------ -- David Roberts School of Mathematical Sciences University of Adelaide SA 5005 ------------------------------------------------------------------------ -- droberts@maths.adelaide.edu.au www.maths.adelaide.edu.au/~droberts