diff --git a/cheatsheet.md b/cheatsheet.md
index 4cdc3b5..e12b301 100644
--- a/cheatsheet.md
+++ b/cheatsheet.md
@@ -41,6 +41,11 @@ binary representation of `x`, taking exactly as many whole bytes as
 needed to unambiguously identify the value and its sign. `intbytes(0)`
 is the empty byte sequence.
 
+When reading, the length of the input is supplied externally. This means
+that, when reading a length/value pair in a `seq()`, each length should
+be passed down to the decoder for the corresponding value, so that the
+decoder knows when to stop.
+
 **Annotations.** To annotate a `Repr` `r` (that *MUST NOT* itself
 already be annotated) with some sequence of `Value`s `[v_1, ..., v_m]`,
 surround `r` as follows: