Index Register usage in Structured Text Programs

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In the operation manual "W447-E1-05 CX-Programmer Ver. 7.2 OPERATION MANUAL Function Blocks/Structured Text" the subject of using IR Index Registers is discussed in Section 2-5-6. I have successfully used IR's in LADDER Function Blocks but cannot for the life of me figure out how to apply them in Structured Text Function Blocks OR Structured Text Tasks. The manual is a bit vague as to whether IR's CAN or CANNOT be used in ST programs. If they CAN there is no clear description as to what syntax is used. Does anyone have any feedback on this issue? Can IR's be used in ST programs? If they can then what syntax is used how and how are IR variables declared? CONFUSED