Theoretically, XML might be a possibility but I wouldn't like to try it
myself.

Bob Phillips wrote:
No, a text file doesn't hold all the detail about formatting. That is partly
why Excel files are much bigger than text files, it contains that formatting
data within it.

There is a Rich Text Format file type (RTF), which holds some formatting
details when opened in Word, but I haven't tried opening one of those in
Excel, but it won't do what you want.