Drawing objects, images, and frames aside, the .CurrentSelection of a Writer document supports the one service com.sun.star.text.TextRanges.
This service exports three intefaces, but none of them allows for any manipulations like adding or removing a TextRange object to/from the container. They only give access.
This is fundamentally different from other cases of .CurrentSelection objects.
Is there a somehow hidden way to create something containing more than one TextRange, and to pass it to the CurrentController for selection? XSearchable obviously knows how to create a TextRanges container for selection.
(The update only tried to clarify the subject, and eliminated a few minor typos.)