with_buffer_and_point contents { col; row } ~f runs f in a temp buffer with contents and point at row and col.

Print buffer contents with the point shown as a solid block.

with_buffer_and_active_region contents region ~f runs f in a temp buffer with contents, mark at region.start, and point at region.end_.

Print buffer contents with the start and the end of the active region replaced by solid blocks.

Print buffer contents with the before-string and after-string properties from any overlays rendered as though they were present in the buffer. Also, mark any text specified as invisible through overlays (but not through text properties). This does not reflect the actual contents of the buffer, but rather how the contents would appear to the user.