diff --git a/docs/formats/core-data-regions.md b/docs/formats/core-data-regions.md
index d137049..10085d1 100644
--- a/docs/formats/core-data-regions.md
+++ b/docs/formats/core-data-regions.md
@@ -185,3 +185,36 @@ less than a structure needs.
 Recorded because the lead was committed as a lead and this is where it goes.
 Nothing else about the region has been identified: it is real, non-zero data
 of unknown type, bounded, and unopened beyond these ~150 bytes.
+
+## The region after shrub has a repeating structure at stride 368
+
+**Range measured:** level 0, `16047040 .. 16737344`, sampled as the first
+65,536 bytes. Cross-checked on every level that has the region, each sampled
+the same way from its own region start.
+
+**Method:** autocorrelation. For each candidate stride, count how often a
+4-byte sequence at offset *i* repeats at *i + stride*, as a fraction of
+comparable positions. A random control of the same size is measured
+identically and reads flat at 0.0000 for every stride, so the statistic
+discriminates.
+
+**Result:**
+
+| stride | region match rate |
+|---|---|
+| 368 | 0.1110 |
+| 340 | 0.0935 |
+| 337–339 | 0.026–0.029 (background) |
+| random control | 0.0000 |
+
+Stride **368** is the strongest peak. On level 0, 340 is a secondary peak
+well clear of the background; the two differ by 28, which is unexplained.
+
+**Cross-check:** the peak stride was recomputed independently for every level
+that has the region, and **all 24 peak at exactly 368**. That is the part
+that makes this worth recording -- a single level's peak could be a property
+of that level's data, but 24 of 24 agreeing is a format invariant.
+
+What a 368-byte record *is* remains unestablished. This is the same position
+the shrub body was in before differential analysis identified its records,
+and the same method is the obvious next step.