feat: 💥 RepresentationOf concept now also accepts a QuantitySpec and accepts any representation character for quantity kinds

docs/users_guide/framework_basics/character_of_a_quantity.md

@@ -148,7 +148,7 @@ As we remember, the `quantity` class template is defined as follows:
 
 ```cpp
 template<Reference auto R,
-         RepresentationOf<get_quantity_spec(R).character> Rep = double>
+         RepresentationOf<get_quantity_spec(R)> Rep = double>
 class quantity;
 ```
 

docs/users_guide/framework_basics/concepts.md

@@ -159,15 +159,28 @@ A `Reference` can either be:
 [value of a quantity](../../appendix/glossary.md#quantity-value).
 
 
-### `RepresentationOf<T, Ch>` { #RepresentationOf }
+### `RepresentationOf<T, V>` { #RepresentationOf }
 
-`RepresentationOf` concept is satisfied by all `Representation` types that are of a specified
-[quantity character](../../appendix/glossary.md#character) `Ch`.
+`RepresentationOf` concept is satisfied:
+
+- if the type of `V` satisfies [`QuantitySpec`](#QuantitySpec):
+
+    - by all [`Representation`](#Representation) types when `V` describes
+      a [quantity kind](../../appendix/glossary.md#kind),
+    - otherwise, by [`Representation`](#Representation) types that are of
+      a [quantity character](../../appendix/glossary.md#character) associated with a provided
+      quantity specification `V`.
+
+- if `V` is of `quantity_character` type:
+
+    - by [`Representation`](#Representation) types that are of a provided
+      [quantity character](../../appendix/glossary.md#character).
 
 A user can declare a custom representation type to be of a specific character by providing the specialization
 with `true` for one or more of the following variable templates:
 
 - `is_scalar<T>`
+- `is_complex<T>`
 - `is_vector<T>`
 - `is_tensor<T>`
 

docs/users_guide/framework_basics/design_overview.md

@@ -316,7 +316,7 @@ This is why a `quantity` class template is defined in the library as:
 
 ```cpp
 template<Reference auto R,
-         RepresentationOf<get_quantity_spec(R).character> Rep = double>
+         RepresentationOf<get_quantity_spec(R)> Rep = double>
 class quantity;
 ```
 
@@ -365,7 +365,7 @@ In the **mp-units** library, the quantity point is implemented as:
 ```cpp
 template<Reference auto R,
          PointOriginFor<get_quantity_spec(R)> auto PO,
-         RepresentationOf<get_quantity_spec(R).character> Rep = double>
+         RepresentationOf<get_quantity_spec(R)> Rep = double>
 class quantity_point;
 ```
 

docs/users_guide/framework_basics/simple_and_typed_quantities.md

@@ -20,7 +20,7 @@ In the **mp-units** library, a quantity is represented with the following class
 
 ```cpp
 template<Reference auto R,
-         RepresentationOf<get_quantity_spec(R).character> Rep = double>
+         RepresentationOf<get_quantity_spec(R)> Rep = double>
 class quantity;
 ```
 

docs/users_guide/framework_basics/the_affine_space.md

@@ -96,7 +96,7 @@ origin:
 ```cpp
 template<Reference auto R,
          PointOriginFor<get_quantity_spec(R)> auto PO = default_point_origin(R),
-         RepresentationOf<get_quantity_spec(R).character> Rep = double>
+         RepresentationOf<get_quantity_spec(R)> Rep = double>
 class quantity_point;
 ```