It pointed out a problem that I would have thought should result in test failure. Code corrected, and documentation updated to describe the unexpected behavior.
Fix#3918, sort of. Xlsx cells use the default style when they omit the `s` tag, or when `s="0"` is specified. LibreOffice does not honor Alignment in the default Style unless the cell explicitly uses the second form, even though it honors other default Styles (e.g. bold font) when `s` is omitted. Gnumeric seems to have the same problem. A bug report has been filed with LibreOffice.
In the meantime, this PR adds to Xlsx Writer an optional boolean property `explicitStyle0` with setter and getter. Default is false, which will continue the current behavior by adding an `s` tag only when the cell uses a non-default style (this is how Excel itself behaves). When set to true, Xlsx Writer will explicity write `s="0"` for all cells using default style. This will allow users to create an Xlsx spreadsheet with default alignment of cells that will show up correctly when the spreadsheet is viewed with LibreOffice. Technically speaking, it is *probably* safe to always use `true`, except that the spreadsheet size will be a bit larger. However, my hope is that this is a temporary measure which can go away when the vendors have had a chance to fix their problems, hence the `false` default.
oleibman