Mapping issue: Split a string to multiple strings in an idoc

Hi,

I need to split a string with an undefined length into strings of 132 chars. The problem is, how to map from the source field to the target field,

which belong to an idoc segment. The segment has the occurence 1 to unbounded, and the field 0 to 1. Simplifying, i need to map one source field split it in 132

chars block and put the resultant blocks into an idoc field (maxLength = 132).

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IDoc

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Segment X

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...

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Segment (occurence 1..unbounded)

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Field X

Source field SourceA (undefined length)---- -> -----Field TargetA (occurence 0..1) (maxLength = 132)

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Segment Y

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...