Update doc pages

Author: odersky

docs/_docs/reference/experimental/capture-checking/classifiers.md

@@ -45,25 +45,28 @@ sealed trait Capability
 trait SharedCapability extends Capability Classifier
 trait Control extends SharedCapability, Classifier
 
-trait ExclusiveCapability extends Capability, Classifier
-trait Mutable extends ExclusiveCapability, Classifier
+trait ExclusiveCapability extends Capability
+trait Read extends ExclusiveCapability, Classifier
 ```
-Here is a graph showing the hierarchy of predefined classifier traits:
+Here is a graph showing the hierarchy of predefined capability traits. Classifier traits are underlined.
 ```
               Capability
               /        \
              /          \
             /            \
            /              \
  SharedCapability     ExclusiveCapability
+ ----------------
         |                    |
         |                    |
         |                    |
         |                    |
-     Control              Mutable
+     Control               Read
+     -------               ----
 ```
-At the top of the hierarchy, we distinguish between _shared_ and _exclusive_ capabilities in two classifier traits `SharedCapability` and `ExclusiveCapability`. All capability classes we have seen so far are shared.
-`ExclusiveCapability` is a base trait for capabilities that allow only un-aliased access to the data they represent, with the rules governed by [separation checking](separation-checking.md). Separation checking is currently an optional extension of capture checking, enabled by a different language import. Since `Capability` is a sealed trait, all capability classes are either shared or exclusive.
+At the top of the hierarchy, we distinguish between _shared_ and _exclusive_ capabilities in two traits `SharedCapability` and `ExclusiveCapability`. All capability classes we have seen so far are shared.
+`ExclusiveCapability` is a base trait for capabilities that
+are checked for anti-aliasing restrictions with the rules governed by [separation checking](separation-checking.md). Separation checking is currently an optional extension of capture checking, enabled by a different language import. Since `Capability` is a sealed trait, all capability classes are either shared or exclusive.
 
 `Control` capabilities are shared. This means they cannot directly or indirectly capture exclusive capabilities such as capabilities that control access to mutable state. Typical `Control` capabilities are:
 

docs/_docs/reference/experimental/capture-checking/mutability.md

@@ -31,9 +31,9 @@ A capability is called
 
 We introduce a new trait
 ```scala
-trait Mutable extends ExclusiveCapability, Classifier
+trait Mutable
 ```
-It is used as a [classifier](classifiers.md) trait for types that define mutable variables and/or _update methods_.
+It is used as a marker trait for types that define mutable variables and/or _update methods_.
 
 ## Update Methods
 
@@ -134,10 +134,9 @@ a method that accesses exclusive capabilities.
 
 If `x` is an exclusive capability of a type extending `Mutable`, `x.rd` is its associated _read-only_ capability. It counts as a shared capability. A read-only capability does not permit access to the mutable fields of a matrix.
 
-A read-only capability can be seen as a classified capability
-using a classifier trait `Read` that extends `Mutable`. I.e.
-`x.rd` can be seen as being essentially the same as `x.only[Read]`.
-(Currently, this precise equivalence is still waiting to be implemented.)
+A read-only capability can be seen as a [classified](classifiers.md) capability
+using a classifier trait `Read`. I.e.
+`x.rd` is a shorthand for `x.only[Read]`.
 
 **Implicitly added capture sets**