If length is 0 then word match type for all words in a search query is controlled only by the value of the "wm" search parameter value.
With a positive length value, the words under the given length are searched using full word match, even if the "wm" search parameter tells to use one of the substring match types: wm=beg, wm=sub or wm=end. This can be useful for performance purposes, when substring match for short words returns too many hits.
Default value is 0.
MaxWordLength, MinWordLength, description of the "wm" search parameter in the Section called Search parameters in Chapter 8.