How to get the value of slopes of pchip at the enpoints?

The doc page pchip (under the Output Arguments, pp section) shows how the interpolationg polynominal is formed for each interval based on the breakpoints and the pp coefficients, from which it should be straighforward to compute the derivative at the leading and trailing edges of the first and last intervals respectively.

x = 0:.1:1;y=sin(x);
pp = pchip(x,y);
pp

pp = struct with fields:
      form: 'pp'
    breaks: [0 0.1000 0.2000 0.3000 0.4000 0.5000 0.6000 0.7000 0.8000 0.9000 1]
     coefs: [10×4 double]
    pieces: 10
     order: 4
       dim: 1

Not sure why pp.oder = 4. That seems odd for a cubic polynomial.