Thanks again. Except for the delegation message it seems to be working formula. However, no results are returned.
Reading what you wrote, as well as some other details I've gleaned in other posts, and I want to allow people to use a search box I tried the following formula.
Filter(Source,StartsWith('Modified By'.Email,TextSearchBox.Text))
This worked like a charm. Now I'll tell the staff to search by their username which is the same as the prefix of their email address before the companies domain name.
Thank you so much for your speedy help.