Byte order mark
An invisible character that some programs write at the very start of a text file to signal its encoding. It is often shortened to BOM.
In a UTF-8 file the mark is optional, and software that does not expect it reads it as part of the data. The usual symptom is a first column whose name looks right and matches nothing.
Where it comes up
- Stray whitespace and invisible charactersTwo values look identical on screen but differ by a trailing space, a non-breaking space, or a hidden character.
- Inconsistent column names across filesFiles that should share one layout name the same column differently, or use the same name for different things.
See also
- UTF-8The most widely used encoding for Unicode text. It stores each character in one to four bytes, with plain English letters and digits taking one byte each.
- EncodingThe rule that maps the bytes in a file to characters. Reading a file with the wrong encoding turns accented letters and symbols into nonsense.
- HeaderThe row at the top of a table that holds the column names. In data files it is normally the first line.