The Spreadsheet has some issues we may want to double check:

• The title attribute present in the column headers (currently is "Sort by"), is read in all rows, in all columns, before the content, it looks like the title attribute should actually be the name of the column for it to be accessible. For example, if your table is:
  Name  |  Species
  Garfield |  Cat

When you focus the "Cat" cell it will read: "Sort by, Cat, column 2".
It should be: "Species, Cat, column 2".

To do this, change the title attribute in the column header to match the column name.

• The headers are clickable, so we should either wrap the buttons + the arrow in <button> tags, or make sure we use the appropiate aria-role to make sure they are interpreted as buttons. Using <button> is probably the best option.
• Make sure the changes in sorting order are properly announced.

I ran into an issue where the Spreadsheet was absolutely ignored by the Screen reader just two times and couldn't reproduce it anymore. Screen readers used to build the "accessibility tree" (imagine it as a simplified version of the page) on page load, but unless I'm wrong they don't works like that anymore and they are aware of DOM changes, I guess it worths testing it reloading the page a few times, maybe altering the bandwidth to test what happens with a slow connection if the spreadsheet takes a while to load.

Copied on Github