Substitutable help classes

Following a discussion with Nikos last month, I've added a new feature to the help system, so that help examples can be modified to be closer to the recognition result. Recall that the help system assumes that the designer will have declared a set of help classes; each class C defines a set of phrases P(C). When choosing a help match, both the recognition result and the help examples are backed off so that, for each class C, phrases in P(C) are replaced by C.

The new functionality I've just added makes it possible to declare some help classes as "substitutable". Suppose that class C is defined as substitutable, that the phrase P1 in the recognition result is backed off to C, and that the phrase P2 in a matched help example H is also backed off to C. In this case, H will not be presented in its original form, but with P2 substituted by P1. Evidently, not all help classes can be defined as substitutable, since it's essential that all the words in a substitutable class have exactly the same syntactic properties.

There are however some important classes which can in general be made substitutable, in particular (at least in English) names for specific types of individual, plural numbers, days of the week and months of the year. I've tested the new functionality on the Calendar app, and it does indeed seem to give considerably more useful responses. Here's an example. Without substitutable classes, the sentence "what meetings has nikos been to" gets the help responses

#1 : "what meetings has pierrette attended in geneva"
     "what meeting_noun has person_name attend_verb preposition loc_name" (backed off)
#2 : "which meetings has elisabeth attended"
     "which meeting_noun has person_name attend_verb" (backed off)
#3 : "what meetings is pierrette going to attend in geneva"
     "what meeting_noun is person_name going to attend_verb preposition loc_name" (backed off)
#4 : "what meetings is pierrette going to attend"
     "what meeting_noun is person_name going to attend_verb" (backed off)
#5 : "what meetings have there been in geneva"
     "what meeting_noun have there been preposition loc_name" (backed off)

With substitutable classes (person_name is one of them), the response is

#1 : "what meetings has nikos attended in geneva"
     "what meeting_noun has person_name attend_verb preposition loc_name" (backed off)
#2 : "which meetings has nikos attended"
     "which meeting_noun has person_name attend_verb" (backed off)
#3 : "what meetings is nikos going to attend in geneva"
     "what meeting_noun is person_name going to attend_verb preposition loc_name" (backed off)
#4 : "what meetings is nikos going to attend"
     "what meeting_noun is person_name going to attend_verb" (backed off)
#5 : "what meetings will nikos attend in geneva"
     "what meeting_noun will person_name attend_verb preposition loc_name" (backed off)

I haven't done any systematic testing, but anecdotally I'm pretty sure that this seems to make help more responsive.