OpenXML Filter: XLSX: Extract groups of textual units per row

The grouping of textual units should be performed in a natural way that will reflect the structure of the document. E.g.:

The extraction would be the following:

GroupEvent
TextUnit A2
TextUnit common
TextUnit C2
TextUnit common
Ending
GroupEvent
TextUnit A3
TextUnit B3
TextUnit common
TextUnit D4
Ending

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