I'm going to use a couple of technical terms here, and you might want to slow me down when I explain this. It's a bit of the reverse onus principle. For many years we tried to have, per occupation, mutual recognition agreements between the occupations across provinces. These processes were fairly intense and convoluted, and were not producing the results we were expecting.
With the reverse onus principle, what we've essentially said is that for regulated occupations, you have full mobility in any occupation, except for a process of transparency called the posting of exceptions. If a provincial government or regulatory agency can convince other provincial governments that, frankly, the standards are so different that there is a material difference between their standards, it can require you to post an exception. It's called supplementary measures or additional measures.