glm fitting.
  Typically only used internally by glm.fit, but may be
  used to construct a control argument to either function.
glm.control(epsilon = 1e-8, maxit = 25, trace = FALSE)control argument of glm is by default passed
  to the control argument of glm.fit, which uses
  its elements as arguments to glm.control: the latter provides
  defaults and sanity checking.  If epsilon is small (less than $1e-10$) it is
  also used as the tolerance for the detection of collinearity in the
  least squares solution.
  When trace is true, calls to cat produce the
  output for each IWLS iteration.  Hence, options(digits = *)
  can be used to increase the precision, see the example.
glm.fit, the fitting procedure used by glm.