The manual (split in this case) can usually dissipate such doubts:

               If the PATTERN contains parentheses, additional
               list elements are created from each matching sub-
               string in the delimiter.
                                                                      
+          
                   split(/([,-])/, "1-10,20", 3);
                                                                      
+          
               produces the list value
                                                                      
+          
                   (1, '-', 10, ',', 20)
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