Boundary conditions in PDE Solver (pdepe)

I try to solve the heat equations following the example given here , but I do not understand how the boundary conditions are applied:

function [pl,ql,pr,qr] = pdex1bc(xl,ul,xr,ur,t)
pl = ul;
ql = 0;
pr = pi * exp(-t);
qr = 1;

For example, how the above code should be altered for the following cases:

1. u(0,t) = 5, u(L,t) = 100 // finite

2. u(0,t) = 5, u(∞, t) = 100 // semi-infinite

3. u_x(0,t) = 5, u_x(L,t) = 0 // finite slab, one side at constant flux, one side insulated

[Bill Greene]

I have some pdepe boundary condition notes that might be of some help.