Undocumented AB property 'com.apple.speech.ABSpeakable'?

FROM : Stefan
DATE : Sun Aug 20 15:42:31 2006

Today, we found a new property in address book:

   com.apple.speech.ABSpeakable

Example values:

"com.apple.speech.ABSpeakable" = {person = 1; speak = 1; useFirst = 
0; useLast = 0; useNickname = 1; };     

Since I've never seen this property before, I suppose the property is 
new in Tiger.

Since this property breaks one of our apps since Tiger, I really 
wonder, why I've never seen this property
in any documentation.

Is this property not documented? Even Google does not know anything 
about 'com.apple.speech.ABSpeakable'.