Text Processing Nodes Accepting Only DocumentCells

Dear Forumers,

I have a question regarding text processing nodes. I want to used them from a table kind of resources that I gained before. I would like to convert a String cell to DocumentCells as it is stated in one of the node help bubbles. This is eg. the Case Converter node, but I cannot convert my data type into DocumentCells.

Can you provide information how this data type gets created?

Thanks,
Balint

You can start with the following node to convert StringCells to DocumentCells: