To check if the input is of a given class.
a Any value.
classname One of the strings specified below.
is true if the the class name of the first input is the same as the one specified.

The following values of className are meaningful:

   'double'      scalars or arrays of real or complex numbers.  
   'char'      character or arrays of characters.  
   'SparseMatrix'      sparse matrix.  
   'structure'      dictionary/map/structure array.  
   'cell'      list of elements of different data types/cell array.  
   'Null'      undefined object.  
   'MClass'      Mathnium Class  
   'MLClass'      Matlab Class.  
   'function'      functions.  
If the input className is the name of a class, be it a Java class, a Mathnium class or a Matlab-type class, the function checks if the first input is an instance of the class.