This is a method for the generic quantile
  function for the class ewcdf of empirical weighted cumulative
  distribution functions.
The quantile for a probability p is computed
  as the right-continuous inverse of the cumulative
  distribution function x (assuming type=1, the default).
If normalise=TRUE (the default),
  the weighted cumulative function x is first normalised to
  have total mass 1 so that it can be interpreted as a
  cumulative probability distribution function.