This is a wordpress plugin written in anticipation of getting a particular contract. I didn't get the contract, but that wasn't the plugin's fault. Other events intervened, and ... well, you know ... sh*t happens.
I had gone ahead and written the plugin because of the import/export spreadsheet aspect of it. I had not worked with PHPSpreadsheet before and was eager to see what I could do with it. I was pleasantly surprised about how easy it was to work with, in spite of the somewhat spotty coverage of the documentation. Actually, it has far better documentation than I had originally expected, but it never seemed to have what I was looking for in one place. And the examples all seemed a little simplistic, not a real world example in any of them. In that vein, the code reading the spreadsheet is in classes/Form/Workbook.php, in the import_nodelist method, and the code writing to a spreadsheet is in classes/Plugin/Nodelist.php, in the write_spreadsheet method. The latter file also contains code emailing the exported spreadsheet to a user, in the email_spreadsheet method.
In the end, I decided to go ahead and make the code available here on github. If you find that the code here helps you out on one of your projects, I just ask that you add a link to this repository in a code comment within your project. It is something I try to do when other people's code helps me out.