address comments

Author: matthias-springer

mlir/include/mlir/IR/BuiltinTypeInterfaces.td

@@ -23,14 +23,20 @@ include "mlir/IR/OpBase.td"
 def VectorElementTypeInterface : TypeInterface<"VectorElementTypeInterface"> {
   let cppNamespace = "::mlir";
   let description = [{
-    Indication that this type can be used as element in vector types.
-
     Implementing this interface establishes a contract between this type and the
-    vector type indicating that this type can be used as element of vectors.
-
-    The interface currently has no methods and is used by types to opt into
-    being vector elements. This may change in the future, in particular to
-    require types to provide their size or alignment given a data layout.
+    vector type, indicating that this type can be used as element of vectors.
+
+    Vector element types are treated as a bag of bits without any assumed
+    structure. The size of an element type must be constant, but it does not
+    necessarily have to be a compile-time constant.
+
+    Note: This type interface is still evolving. It currently has no methods
+    and is just used as marker to allow types to opt into being vector elements.
+    This may change in the future, for example, to require types to provide
+    their size or alignment given a data layout. Please post an RFC before
+    adding this interface to additional types. Implementing this interface on
+    downstream types is discourged, until we specified the exact properties of
+    a vector element type in more detail.
   }];
 }