diff --git a/src/main.org b/src/main.org
index bc97bcfb38a7030910be3f797918f485b1c5a6f3..d24621ce5894e369d738890d4acda64e4609eb55 100644
--- a/src/main.org
+++ b/src/main.org
@@ -237,7 +237,7 @@ Samples taken for an entity must be represented as datasets with the length repr
 
 Missing float samples must be represented by /NaN/ values.
 
-An entity must have a 2-dimensional 32-bit float dataset named /poses/, representing the entity's poses with axes time and coordinate. If the dataset's length is \(1\), the entity is considered /fixed in place/.
+An entity may have a 2-dimensional 32-bit float dataset named /poses/, representing the entity's poses with axes time and coordinate. If the dataset's length is \(1\), the entity is considered /fixed in place/.
 
 An entity may contain a 3-dimensional 32-bit float dataset named /outlines/, representing the entity's outlines with the axes time, point, and coordinate. Any outline with less points than the size of /outlines/' second dimension must pad with trailing /NaN/ coordinates. If the dataset's length is \(1\), the entity is considered to have a /fixed outline/.