Is it possible to append content to an .xls file using PHP fwrite()?
When i try this using fwrite(), the resulting file causes an error message in Excel 2007.
Is there a specific separator I can use to accomplish this?
Is it possible without a third party library?
You can use the PhpSpreadsheet library, to read an existing Excel file, add new rows/columns to it, then write it back as a real Excel file.
Disclaimer: I am one of the authors of this library.