FTR: tdf#155918, which also describes why “split window” does not make sense for Writer. Basically, splitting window implies alignment, which makes no sense for Writer’s variable pages/paragraphs (and multi-page views), while being perfectly sensible for column-based Calc sheets (but note how you can’t split Calc document to have different sheets in different sub-windows).
Note that “If you say this, I guess you didn’t ever work with a long document” is a silly attempt to suppress other’s words. We all have worked with different documents; and if you didn’t feel comfortable with a specific workflow, doesn’t necessarily mean you did that right, or that others couldn’t sensibly use it, maybe using a better DE
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