Named at a line somebody chose.

Between nothing and everything

04.03.04 dealt with a body that covers another completely. But two sessions can stand in every intermediate relation as well — the second recovering a tenth of the first, or half, or nine-tenths.

Containment is a spectrum, and the patterns in this lesson are names for a region of it. A piercing line is a falling session followed by a rising one that opens below the first's low and closes more than halfway up the first body, without covering it. Dark cloud cover is the mirror after a rise.

Everything about those definitions is measurable. What is not measurable is why the line sits at half.

The threshold is a convention

This is the point the lesson exists for, and it generalises far beyond these two patterns.

The 50% line is not a finding. Nobody measured a great many sessions, discovered that markets behave differently either side of the midpoint, and reported it. Somebody chose a round number, wrote it down, and it was copied.

You can tell it is a convention by what happens at the edges. A close at 49.5% of the first body and a close at 50.5% describe sessions that are, in every respect a reader could check, the same. One has a famous name and one has none.

That is not an argument against the name. A shared vocabulary is useful, and "piercing line" is much quicker than the sentence it stands for. It is an argument against treating the name as though it were a property of the market rather than of the language.

A threshold in a pattern definition is a decision about vocabulary. It is not a discovery about price.

The weaker cousins, and why they exist

The literature is quite honest about the spectrum, because it has names for the shallower cases too. A rising session that closes only at or barely into the first body is called an on-neck or in-neck line; one that gets further but still short of the midpoint is a thrusting line.

Read as a group they make the structure obvious: on-neck, in-neck, thrusting, piercing, engulfing is one continuum of how far the second session got, cut into five labelled pieces.

Which is the useful way to hold all of them. Rather than five patterns to memorise, there is one measurement — how far into the first body the second session closed — and a set of names for regions of it, exactly as chapter 04.02 was names for regions of close location.

One measurement, cut into named regions by lines somebody drew. The next lesson takes three boards instead of two — and then does something to them that makes the whole chapter shrink.