+ /**
+ * Finds and displays cross-references for the selected sequences (protein
+ * products for nucleotide sequences, dna coding sequences for peptides).
+ *
+ * @param sel
+ * the sequences to show cross-references for
+ * @param dna
+ * true if from a nucleotide alignment (so showing proteins)
+ * @param source
+ * the database to show cross-references for
+ */