11.1.2.3.2 Notes about The KEYWORD Package

It is generally best to confine the use of keywords to situations in which there are a finitely enumerable set of names to be selected between. For example, if there were two states of a light switch, they might be called :on and :off.

In situations where the set of names is not finitely enumerable (i.e., where name conflicts might arise) it is frequently best to use symbols in some package other than KEYWORD so that conflicts will be naturally avoided. For example, it is generally not wise for a program to use a keyword[1] as a property indicator, since if there were ever another program that did the same thing, each would clobber the other's data.