diff --git a/eo-phi-normalizer/grammar/EO/Phi/Syntax.cf b/eo-phi-normalizer/grammar/EO/Phi/Syntax.cf
index 36ce7fb2d..1fdda8502 100644
--- a/eo-phi-normalizer/grammar/EO/Phi/Syntax.cf
+++ b/eo-phi-normalizer/grammar/EO/Phi/Syntax.cf
@@ -27,7 +27,7 @@ separator Binding "," ;
 Phi.    Attribute ::= "φ" ;   -- decoratee object
 Rho.    Attribute ::= "ρ" ;   -- parent object
 Sigma.  Attribute ::= "σ" ;   -- home object
-VTX.    Attribute ::= "ν" ;   -- ???
+VTX.    Attribute ::= "ν" ;   -- an object that represents the unique identifier of the containing object
 Label.  Attribute ::= LabelId ;
 Alpha.  Attribute ::= AlphaIndex ;