In most cases its best to rely on the defaults for ``MB_PYTHON_OSX_VER`` and ``PLAT``, rather than setting them explicitly. Examples of exceptions to this guideline include:
* setting ``MB_PYTHON_OSX_VER=10.6`` to build a 10.6 64/32-bit CPython wheel for Python 2.7 (default for 2.7 is 10.9 64-bit)
* setting ``MB_PYTHON_OSX_VER=10.6 and PLAT=x86_64``to build a 10.6 64-bit only wheel (10.6 would normally be 64/32-bit). Such a wheel would still have a platform tag of ``macosx_10_6_intel`, advertisting support for both 64 and 32-bit, but wouldnt work in 32-bit mode. This may be OK given how unlikely it is that there is still anyone actually running Python on macOS in 32-bit mode.
* setting ``MB_PYTHON_OSX_VER=10.6 and PLAT=x86_64``to build a 10.6 64-bit only wheel (10.6 would normally be 64/32-bit). Such a wheel would still have a platform tag of ``macosx_10_6_intel`, advertisting support for both 64 and 32-bit, but wouldnt work in 32-bit mode. This may be OK given how unlikely it is that there is still anyone actually running Python on macOS in 32-bit mode.
The ``build_wheel`` function builds the wheel, and ``install_run``
function installs and tests it. Look in ``multibuild/common_utils.sh`` for
