Specify the mapping between tuple types and ValueTuple normatively.

Alternative to #798.

standard/types.md

@@ -389,9 +389,10 @@ An enumeration type is a distinct type with named constants. Every enumeration t
 
 ### 8.3.11 Tuple types
 
-A tuple type represents an ordered, fixed-length sequence of values with optional names and individual types. The number of elements in a tuple type is referred to as its ***arity***. A tuple type is written `(T1 I1, ..., Tn In)` with n ≥ 2, where the identifiers `I1...In` are optional ***tuple element names***. This syntax is shorthand for a type constructed with the types `T1...Tn` from `System.ValueTuple<...>`, which shall be a set of generic struct types capable of expressing tuple types of any arity greater than one.
+A tuple type represents an ordered, fixed-length sequence of values with optional names and individual types. The number of elements in a tuple type is referred to as its ***arity***. A tuple type is written `(T1 I1, ..., Tn In)` with n ≥ 2, where the identifiers `I1...In` are optional ***tuple element names***.
 
-> *Note*: There does not need to exist a `System.ValueTuple<...>` declaration that directly matches the arity of any tuple type with a corresponding number of type parameters. Instead, larger tuples can be represented with a special overload `System.ValueTuple<..., TRest>` that in addition to tuple elements has a `Rest` field containing a nested tuple value of the remaining elements. Such nesting may be observable in various ways, e.g. via the presence of a `Rest` field. *end note*
+This syntax is shorthand for a type constructed with the types `T1...Tn` from `System.ValueTuple<...>`, which shall be a set of generic struct types capable of directly expressing tuple types of any arity between two and seven inclusive.
+Tuple types with an arity of more than seven are constructed There does not need to exist a `System.ValueTuple<...>` declaration that directly matches the arity of any tuple type with a corresponding number of type parameters. Instead, larger tuples can be represented with a generic struct type `System.ValueTuple<T1 I1, ..., T7 I7, TRest>` that in addition to tuple elements has a `Rest` field containing a nested value of the remaining elements, using another `System.ValueTuple<...>` type. Such nesting may be observable in various ways, e.g. via the presence of a `Rest` field. Where only a single additional field is required, the generic struct type `System.ValueTuple<T1>` is used; this type is not considered a tuple type in itself. Where more than seven additional fields are required, `System.ValueTuple<T1 I1, ..., T7 I7, TRest>` is used recursively.
 
 Element names within a tuple type shall be distinct. A tuple element name of the form `ItemX`, where `X` is any sequence of non-`0`-initiated decimal digits that could represent the position of a tuple element, is only permitted at the position denoted by `X`.