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+macro
+-----
+
+Start recording a macro for later invocation as a command::
+
+  macro(<name> [arg1 [arg2 [arg3 ...]]])
+    COMMAND1(ARGS ...)
+    COMMAND2(ARGS ...)
+    ...
+  endmacro(<name>)
+
+Define a macro named ``<name>`` that takes arguments named ``arg1``,
+``arg2``, ``arg3``, (...).
+Commands listed after macro, but before the matching
+:command:`endmacro()`, are not invoked until the macro is invoked.
+When it is invoked, the commands recorded in the macro are first
+modified by replacing formal parameters (``${arg1}``) with the arguments
+passed, and then invoked as normal commands.
+In addition to referencing the formal parameters you can reference the
+values ``${ARGC}`` which will be set to the number of arguments passed
+into the function as well as ``${ARGV0}``, ``${ARGV1}``, ``${ARGV2}``,
+...  which will have the actual values of the arguments passed in.
+This facilitates creating macros with optional arguments.
+Additionally ``${ARGV}`` holds the list of all arguments given to the
+macro and ``${ARGN}`` holds the list of arguments past the last expected
+argument.
+Referencing to ``${ARGV#}`` arguments beyond ``${ARGC}`` have undefined
+behavior. Checking that ``${ARGC}`` is greater than ``#`` is the only
+way to ensure that ``${ARGV#}`` was passed to the function as an extra
+argument.
+
+See the :command:`cmake_policy()` command documentation for the behavior
+of policies inside macros.
+
+Macro Argument Caveats
+^^^^^^^^^^^^^^^^^^^^^^
+
+Note that the parameters to a macro and values such as ``ARGN`` are
+not variables in the usual CMake sense.  They are string
+replacements much like the C preprocessor would do with a macro.
+Therefore you will NOT be able to use commands like::
+
+ if(ARGV1) # ARGV1 is not a variable
+ if(DEFINED ARGV2) # ARGV2 is not a variable
+ if(ARGC GREATER 2) # ARGC is not a variable
+ foreach(loop_var IN LISTS ARGN) # ARGN is not a variable
+
+In the first case, you can use ``if(${ARGV1})``.
+In the second and third case, the proper way to check if an optional
+variable was passed to the macro is to use ``if(${ARGC} GREATER 2)``.
+In the last case, you can use ``foreach(loop_var ${ARGN})`` but this
+will skip empty arguments.
+If you need to include them, you can use::
+
+ set(list_var "${ARGN}")
+ foreach(loop_var IN LISTS list_var)
+
+Note that if you have a variable with the same name in the scope from
+which the macro is called, using unreferenced names will use the
+existing variable instead of the arguments. For example::
+
+ macro(_BAR)
+   foreach(arg IN LISTS ARGN)
+     [...]
+   endforeach()
+ endmacro()
+
+ function(_FOO)
+   _bar(x y z)
+ endfunction()
+
+ _foo(a b c)
+
+Will loop over ``a;b;c`` and not over ``x;y;z`` as one might be expecting.
+If you want true CMake variables and/or better CMake scope control you
+should look at the function command.