Running highest or lowest value of source since the start of the run or since entry.

extreme chooses the maximum or the minimum and since the starting point. With since: "start" (the default) it updates at the end of every bar, warm-up included, so a rule deciding at the close of bar t sees the extreme through bar t-1; a scheduled rule sees its frame bar included. With since: "entry" it is unset while flat, resets when a position opens from flat (not on a scale-in or a partial exit; a reversal opens from flat) and updates before decisions on each bar while invested, so a rule sees the extreme through the current bar. Absent values of source are skipped, and an unset value makes a comparison over it unknown. It keeps its state across a paper session's restarts. since: "entry" is refused in a signal scan, as every operation on the open position is.

Known gaps it inherits: a raw trailing ratchet built from it does not reset after it fires, since: "entry" folds in the whole bar of a mid-bar scheduled fill, and the reset runs only for the entry rule that filled. A since: "entry" value is refused anywhere inside a gate: a gate is evaluated while flat as well as invested, so a value that resets at entry cannot be kept correct there. Use since: "start", or put the condition on an exit. It returns the unit of source.

Example, the highest high since entry, to place a trailing exit under: {"kind": "tracked", "source": {"kind": "price", "field": "high"}, "extreme": "max", "since": "entry"} compared with close using <.