SYLK files that are just CSV files with ID as the first few characters. CSV files can also have ID as the first few characters.
You are Excel, a widely used (and mis-used) application for reading in .csv files. You encounter a file with ID as the first two characters.
- Check the next character to see if it is a comma, thereby reading in the file as a CSV and not a SYLK file
- Offer a choice to the user of loading the file as a SYLK or CSV file, naturally assuming the user knows what the hell a STLK file is in the first place
- Try loading the file as a SYLK file and proceed to shit the bed.
Trick question! You're Excel! Of course you shit the bed. Is there really any other choice?
Note: When your Wikipedia article only references links that show how your product shits the bed it might be time to rethink your strategy.