def add(self, observableElement):
if observableElement not in self._observables:<EOL><INDENT>self._observables.append(observableElement)<EOL><DEDENT>else:<EOL><INDENT>raise RuntimeError(<EOL>"<STR_LIT>"<EOL>.format(observableElement))<EOL><DEDENT>
add an observable element

:param str observableElement: the name of the observable element
:raises RuntimeError: if element name already exist in the store