This increases the chance of hitting the correct letter when typing a word
that exists in the dictionary, rather than only correct it after the fact.
It is most effective after 2 or 3 letters of a word have been typed and gets
more accurate with more typed letters in the word.
If 2 adjacent letters have similar probabilities of occuring, then there is no
hit correction applied.
Amith Yamasani
The Android Open Source Project