I googled for the module, and apparently others have reported the same thing as a bug. Maybe the author, was just using those strings as constants in the equalities for clarity in the incomplete examples, but didn't show where he declared them as constants earlier in the script. As a matter of fact, this has to be the case, because the equalities are using numerical comparisons, i.e. == and != on the strings. So they would have to be constants, otherwise he would use eq and ne in the comparisons.