debian man page for is

is(3itcl)							    [incr Tcl]								 is(3itcl)

NAME
       is - test argument to see if it is a class or an object

SYNOPSIS
       itcl::is option ?arg arg ...?

DESCRIPTION
       The is command is used to check if the argument given is a class or an object; depending on the option given. If the argument if a class or
       object, then 1 is returned. Otherwise, 0 is returned.  The is command also recognizes the commands wrapped in the itcl code command.

       The option argument determines what action is carried out by the command.  The legal options (which may be abbreviated) are:

       is class command
	      Returns 1 if command is a class, and returns 0 otherwise.

	      The fully qualified name of the class needs to be given as the command argument. So, if a class resides in  a  namespace,  then  the
	      namespace needs to be specified as well. So, if a class C resides in a namespace N, then the command should be called like: is N::C
		  or is ::N::C

       is object ?-class className? command
	      Returns 1 if command is an object, and returns 0 otherwise.

	      If  the  optional "-class" parameter is specified, then the command will be checked within the context of the class given. Note that
	      className has to exist. If not, then an error will be given. So, if className is uncertain to be a class, then the  programmer  will
	      need to check it's existance beforehand, or wrap it in a catch statement.

	      So,  if  c  is  an  object in the class C, in namespace N then these are the possibilities (all return 1): set obj [N::C c] itcl::is
	      object N::c itcl::is object c itcl::is object $obj itcl::is object [itcl::code c]

KEYWORDS
       class, object

itcl									3.3								 is(3itcl)