Table 2. Summary of variables used by the explanation method.

Variable	Description
i, X	input sequence index and input sequence
t, T	token index and token sequence
f, F	feature and set of features
Y	label sequence
j, R	region index in sentence and set of regions
π, Π	perturbed sentence and set of perturbed sentences
k, K	label k and number of labels
$e_{ij}^{k\star }$	explanation vector for region j in sentence i for label k