// pattern for use in texture/pigment
// this pattern can only be used when applied to an object
// value is influenced by the slope of the object
  slope
    y,              // direction vector for slope
    //y,            // optional: dependency from altitude
    //<0.5,1.0>,    // optional: range of slope values
    //<0.75,1.0>    // optional: range of altitude values


// alternativly (new in 3.7): 
/* 
slope { point_at <ReferencePoint> [, Lo_Slope, Hi_Slope] }
  
  (Note that this variant currently does *not* allow for the "altitude" keyword to be used.)
	
      The functionality is similar to MegaPOV's "aoi <ReferencePoint>" pattern, 
      except that the values are reversed, i.e. range from 0.0 for surfaces 
      facing away from the point in question, to 1.0 for surfaces facing towards 
      that point; thus, "slope { <Vector> }" and "slope { point_at 
      <Vector>*VeryLargeNumber }" have virtually the same effect.
*/