The specified number n of random points is
  generated with uniform distribution on the network L.
  The random points are generated using runifpointOnLines.
If n is an integer vector, then a multitype point pattern is
  generated, with n[i] random points of type i.
  
If ex is given, then it serves as an example for determining
  n and L. The default value of n
  will be the number of points in ex
  (or the number of points of each type in ex if it is
  multitype).
  The default value of L will be 
  the network on which ex is defined.