Add inline documentation for Type and DataType. (#24561)

* Add inline documentation for Type and DataType.

Closes #23655.

* Fix type annotation and clean up examples

* Apply suggestions from code review

Co-authored-by: Matt Bauman <mbauman@gmail.com>

Co-authored-by: Matt Bauman <mbauman@gmail.com>

Author: phrb

base/docs/basedocs.jl

@@ -1130,6 +1130,56 @@ The singleton type containing only the value `Union{}` (which represents the emp
 """
 Core.TypeofBottom
 
+"""
+    Core.Type{T}
+
+`Core.Type` is an abstract type which has all type objects as its instances.
+The only instance of the singleton type `Core.Type{T}` is the object
+`T`.
+
+# Examples
+```jldoctest
+julia> isa(Type{Float64}, Type)
+true
+
+julia> isa(Float64, Type)
+true
+
+julia> isa(Real, Type{Float64})
+false
+
+julia> isa(Real, Type{Real})
+true
+```
+"""
+Core.Type
+
+"""
+    DataType <: Type{T}
+
+`DataType` represents explicitly declared types that have names, explicitly
+declared supertypes, and, optionally, parameters.  Every concrete value in the
+system is an instance of some `DataType`.
+
+# Examples
+```jldoctest
+julia> typeof(Real)
+DataType
+
+julia> typeof(Int)
+DataType
+
+julia> struct Point
+           x::Int
+           y
+       end
+
+julia> typeof(Point)
+DataType
+```
+"""
+Core.DataType
+
 """
     Function
 

doc/src/base/base.md

@@ -147,6 +147,8 @@ Base.identity
 
 ```@docs
 Base.supertype
+Core.Type
+Core.DataType
 Core.:(<:)
 Base.:(>:)
 Base.typejoin