Add comment to document the odd constructor usage.

Author: johann-petrak

src/gate/plugin/learningframework/data/CorpusRepresentationMalletTarget.java

@@ -165,6 +165,7 @@ static Instance extractIndependentFeaturesHelper(
           Pipe pipe) {
 
     AugmentableFeatureVector afv = new AugmentableFeatureVector(pipe.getDataAlphabet());
+    // Constructor parms: data, target, name, source
     Instance inst = new Instance(afv, null, null, null);
     for(FeatureSpecAttribute attr : featureInfo.getAttributes()) {
       FeatureExtraction.extractFeature(inst, attr, inputAS, instanceAnnotation);