preprocessor: submodule update and doc update

doc/manual/source/the-model-file.rst

@@ -10482,6 +10482,23 @@ directive (see below). A function is evaluated at the time it is invoked, not
 at define time. Functions can be included in expressions and the operators that
 can be combined with them depend on their return type.
 
+.. rubric:: Checking variable type
+
+Given a variable name or literal, you can check the type it evaluates to using
+the following functions: ``isboolean``, ``isreal``, ``isstring``, ``istuple``,
+and ``isarray``.
+
+    *Examples*
+
++---------------------+------------+
+| **Code**            | **Output** |
++=====================+============+
+| ``isboolean(0)``    | ``false``  |
++---------------------+------------+
+| ``isboolean(true)`` | ``true``   |
++---------------------+------------+
+| ``isreal("str")``   | ``false``  |
++---------------------+------------+
 
 .. rubric:: Casting between types
 

preprocessor @ 273c54f7

-Subproject commit ff6eea7f297cdceab7b8c2fd954d7332bb86e04f
+Subproject commit 273c54f7fbd9a8f345e33300e25ea5fb45b2b3c8