These functions search for interned symbols
whose names contain the substring string.
For apropos, as each such symbol is found,
its name is printed on standard output.
if such a symbol is defined as a function or dynamic variable,
information about those definitions might also be printed.
no output occurs as the search proceeds;
instead a list of the matching symbols is returned when the search is complete.
If package is non-nil,
only the symbols accessible in that package are searched;
otherwise all symbols accessible in any package are searched.
Because a symbol might be available
by way of more than one inheritance path,
apropos might print information about the same symbol more than once,
or apropos-list might return a list containing duplicate symbols.
Whether or not the search is case-sensitive is implementation-defined.