Toolboxes and MATLAB "lanaguage"

It seems like people wanted more changes to the MATLAB "language" than we saw in the release of R2012b. It is not clear to me what the MATLAB language is. I think of it as the core underlying proprietary code. There is even some proprietary code that I don't consider part of the MATLAB language. I think my view might be as narrow as the MATLAB language is defined by the built-in functions. I particularly interested in how the toolboxes fit into the definition of the lanaguage.