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blackbox/isa  Class detection with sub-type support
   isa(BB,'blackbox') returns true if BB is a black-box operator.

   The black-box variant is extended so you can test if an operator has a
   specific type. Sub-types are separated by a colon:

   If you do not provide a type, anything will be matched. For instance
   isa(BB,':counter') is equivalent to the second example.

   If a type has qualifiers, you may also match those. For example
   isa(BB,':matrix:sparse') is true if BB represents a sparse
   Matlab matrix.

   See also isa.