OLGModel14 documentation needs to explain ShareIssuance equilibrium

[MichaelTiemann]

I can see in the code that:

GeneralEqmEqns.ShareIssuance = @(Sissued,P0,D,tau_cg,tau_d,r) P0-((((1-tau_cg)*P0 + (1-tau_d)*D)/(1+r-tau_cg))-Sissued); % P0=P-S, but substitute for P (see derivation inside the return fn)

And I can understand (by reading OLGModel14_HouseholdReturnFn.m) that P is ((1-tau_cg)*P0 + (1-tau_d)*D)/(1+r-tau_cg) so that the code is claiming that P0 = P-S, and that Ps are prices and S is shares issued, and that S should balance to 1, but I don't understand why the relationship between P0, P, and S would be this. It would be great to see this elaborated in the pdf documentation.