You mean justified alignment in which the widths of the spaces are adjusted so that the cell text is aligned at both left and right sides?
No, with fill horizontal alignment, the text cell value is repeated so it fills the cell width
Thank you very much for the picture and explanation bpranoto.You have thought me something new about spreadsheets (at least about formatting cells) (I never used that feature before)As far as I know fpspreadsheet (currently) does not have provision for that. As author wp is able to tell more.