option
------
Provide a boolean option that the user can optionally select.
.. code-block:: cmake
option(<variable> "<help_text>" [value])
If no initial ``<value>`` is provided, boolean ``OFF`` is the default value.
If ``<variable>`` is already set as a normal or cache variable,
then the command does nothing (see policy :policy:`CMP0077`).
For options that depend on the values of other options, see
the module help for :module:`CMakeDependentOption`.
In CMake project mode, a boolean cache variable is created with the option
value. In CMake script mode, a boolean variable is set with the option value.