Definition
Plain language
The marker that says where one piece of text stops and the next begins.
As stated in the literature
A character or token sequence used to separate records or fields in a serialized format; if untrusted content can emit the delimiter, it can forge structure in the surrounding document.
Also called: delimiters
Why it matters: Whenever untrusted text is dropped into a structured document, the delimiter is the seam an attacker will try to pry open to forge structure that was never really there.
For example, in a file where each line is one record, the line break is the delimiter — and if someone's name field contains a line break, they can make one record look like two.
Heard on the show
“Stage two is short and almost boring by comparison — a small supervised set that teaches the model to package the foresight in clean delimiters before it acts.”Episode 183 — Why You Can't Fine-Tune Foresight Into an AI Agent