The flat file is delimited by a square character. What is this character called?
Bytes in a file can be one of 256 characters (hex codes 00 to FF), however, not all characters are
printable.
What is displayed for an
unprintable character depends on the font used to view the file - but most fonts will display the square character.
To see the hex code of the character, you could view the file in Vertical Hex Mode (Alt+J). The 2 lines underneath the text line contain the corresponding hex code for each character.
Alternatively, you can simply left-click on the box character, and while the button is clicked, the hex (and decimal) character code will be displayed in the bottom left of the status bar.
