The action code tells @key{Mouse-1} how to follow the link:
@table @asis
-@item a string
+@item a string or vector
If the action code is a string or vector, the @key{Mouse-1} event is
translated into the first element of the string or vector; i.e., the
action of the @key{Mouse-1} click is the local or global binding of
-that character. Thus, if the action code is @code{"foo"},
+that character or symbol. Thus, if the action code is @code{"foo"},
@key{Mouse-1} translates into @kbd{f}. If it is @code{[foo]},
@key{Mouse-1} translates into @key{foo}.