01  ROOT-GROUP.
          05  FLD   OCCURS 7 TIMES
                    INDEXED BY A1
                               A2.
              10  B1  PIC X(1).

Syntax error in the copybook at line 5: Invalid input 'A2' at position 5:31
za.co.absa.cobrix.cobol.parser.exceptions.SyntaxErrorException: Syntax error in the copybook at line 5: Invalid input 'A2' at position 5:31
	at za.co.absa.cobrix.cobol.parser.antlr.ThrowErrorStrategy.recover(ANTLRParser.scala:38)
	at za.co.absa.cobrix.cobol.parser.antlr.copybookParser.item(copybookParser.java:3240)
	at za.co.absa.cobrix.cobol.parser.antlr.copybookParser.main(copybookParser.java:216)
	at za.co.absa.cobrix.cobol.parser.antlr.ANTLRParser$.parse(ANTLRParser.scala:82)
	at za.co.absa.cobrix.cobol.parser.CopybookParser$.parseTree(CopybookParser.scala:224)