Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help issubfield”.

  ISSUBFIELD tests for the presence of a field in a structure just like the standard
  Matlab ISFIELD function, except that you can also specify nested fields
  using a '.' in the fieldname. The nesting can be arbitrary deep.
 
  Use as
    f = issubfield(s, 'fieldname')
  or as
    f = issubfield(s, 'fieldname.subfieldname')
 
  This function returns true if the field is present and false if the field
  is not present.
 
  See also ISFIELD, GETSUBFIELD, SETSUBFIELD