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An invisible character at the head of a file, declaring encoding.
Also known as: BOM, Byte-order mark, Encoding signature, Invisible character at the start of a file
The byte order mark declares a file's encoding and byte order by appearing first. In UTF-8 it is unnecessary — there is no byte order to declare — and its presence there is a frequent source of bugs, because software that does not expect it reads it as content.
Denotes a character placed at the start of a text file to signal its encoding and byte order.
Contexts: Software
Is unnecessary in UTF-8, which has no byte order to declare, and its presence there is a documented source of software faults where it is read as content.
Contexts: Software
Is the same code point as the zero width no-break space, which is why its function depends entirely on its position at the start of a file.
Contexts: Software
No visible form and no drawn shape at all: the character occupies zero width and is rendered as nothing, detectable only by inspecting a file's opening bytes.