diff --git a/Snippets/ExampleExpressions.swift b/Snippets/ExampleExpressions.swift
index ced986e..e160275 100644
--- a/Snippets/ExampleExpressions.swift
+++ b/Snippets/ExampleExpressions.swift
@@ -3,13 +3,18 @@ import MongoQL
 
 func ExampleExpressions()
 {
-    let _:BSON.Document = .init(BSON.Key.self)
+    enum Alphabet:String
     {
-        $0["_"] = [] as [Never]
-        $0["_"] = [:]
-        $0["_"](BSON.Key.self)
+        case a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z
+    }
+
+    let _:BSON.Document = .init(Alphabet.self)
+    {
+        $0[.a] = [] as [Never]
+        $0[.b] = [:]
+        $0[.c](Alphabet.self)
         {
-            $0["_"](BSON.Key.self)
+            $0[.a](BSON.Key.self)
             {
                 $0["_"] = [:]
             }
@@ -27,343 +32,167 @@ func ExampleExpressions()
             $0[+] = 56
         }
     }
-    let _:BSON.Document = .init(BSON.Key.self)
+    let _:BSON.Document = .init(Alphabet.self)
     {
-        $0["_"] =  nil as            Never??
-        $0["_"] = (nil as Never?) as Never??
-        $0["_"] = false
-        $0["_"] = true
-        $0["_"] = [] as [Never]
-        $0["_"] = [:]
-        $0["_"](Int.self)
+        $0[.a] =  nil as            Never??
+        $0[.b] = (nil as Never?) as Never??
+        $0[.c] = false
+        $0[.d] = true
+        $0[.e] = [] as [Never]
+        $0[.f] = [:]
+        $0[.g](Int.self)
         {
             $0[+] = 0
         }
-        $0["_"](BSON.Key.self)
+        $0[.h](BSON.Key.self)
         {
             $0["_"] = 0
         }
-        $0["_"] = .expr
+    }
+
+    let _:Mongo.SetDocument<Alphabet> = .init
+    {
+        $0[.a]
         {
             $0[.in] = (0, .init
             {
                 $0[+] = 0
             })
         }
-        $0["_"] = .expr
+        $0[.b]
         {
-            $0[.abs] = .expr
+            $0[.abs]
             {
                 $0[.abs] = "$field"
             }
         }
     }
-    let _:Mongo.Expression = .expr
+    let _:Mongo.SetDocument<Alphabet> = .init
     {
-        $0[.abs] = .expr
-        {
-            $0[.abs] = "$field"
-        }
+        $0[.a] { $0[.abs] = "$field" }
+        $0[.b] { $0[.add] = "$a" }
+        $0[.c] { $0[.add] = ("$a", "$b") }
+        $0[.d] { $0[.add] = ("$a", "$b", "$c") }
+        $0[.e] { $0[.add] = ["$a"] }
+        $0[.f] { $0[.add] { $0[+] = "$a" } }
+        $0[.g] { $0[.ceil] = "$field" }
+        $0[.h] { $0[.divide] = ("$field", by: 2) }
+        $0[.i] { $0[.exp] = "$field" }
+        $0[.j] { $0[.floor] = "$field" }
+        $0[.k] { $0[.ln] = "$field" }
+        $0[.l] { $0[.log] = (base: 2, of: "$field") }
+        $0[.m] { $0[.log10] = "$field" }
+        $0[.n] { $0[.mod] = ("$field", by: 2) }
+        $0[.o] { $0[.multiply] = "$a" }
+        $0[.p] { $0[.multiply] = ("$a", "$b") }
+        $0[.q] { $0[.pow] = (base: 2, to: "$field") }
+        $0[.r] { $0[.round] = "$field" }
+        $0[.s] { $0[.round] = ("$field", places: 2) }
+        $0[.t] { $0[.sqrt] = "$field" }
+        $0[.u] { $0[.subtract] = ("$field", minus: 2) }
+        $0[.v] { $0[.trunc] = "$field" }
+        $0[.w] { $0[.trunc] = ("$field", places: 2) }
     }
-    let _:BSON.Document = .init(BSON.Key.self)
-    {
-        $0["_"] = .expr
-        {
-            $0[.abs] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.add] = "$a"
-        }
-        $0["_"] = .expr
-        {
-            $0[.add] = ("$a", "$b")
-        }
-        $0["_"] = .expr
-        {
-            $0[.add] = ("$a", "$b", "$c")
-        }
-        $0["_"] = .expr
-        {
-            $0[.add] = ["$a"]
-        }
-        $0["_"] = .expr
-        {
-            $0[.add] = .init
-            {
-                $0[+] = "$a"
-            }
-        }
-        $0["_"] = .expr
-        {
-            $0[.ceil] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.divide] = ("$field", by: 2)
-        }
-        $0["_"] = .expr
-        {
-            $0[.exp] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.floor] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.ln] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.log] = (base: 2, of: "$field")
-        }
-        $0["_"] = .expr
-        {
-            $0[.log10] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.mod] = ("$field", by: 2)
-        }
-        $0["_"] = .expr
-        {
-            $0[.multiply] = "$a"
-        }
-        $0["_"] = .expr
-        {
-            $0[.multiply] = ("$a", "$b")
-        }
-        $0["_"] = .expr
-        {
-            $0[.pow] = (base: 2, to: "$field")
-        }
-        $0["_"] = .expr
-        {
-            $0[.round] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.round] = ("$field", places: 2)
-        }
-        $0["_"] = .expr
-        {
-            $0[.sqrt] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.subtract] = ("$field", minus: 2)
-        }
-        $0["_"] = .expr
-        {
-            $0[.trunc] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.trunc] = ("$field", places: 2)
-        }
-    }
-    let _:BSON.Document = .init(BSON.Key.self)
+
+    let _:Mongo.SetDocument<Alphabet> = .init
     {
-        $0["_"] = .expr
-        {
-            $0[.cmp] = ("$x", 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.eq] = ("$x", 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.gt] = ("$x", 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.gte] = ("$x", 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.lt] = ("$x", 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.lte] = ("$x", 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.ne] = ("$x", 0)
-        }
+        $0[.a] { $0[.cmp] = ("$x", 0) }
+        $0[.b] { $0[.eq] = ("$x", 0) }
+        $0[.c] { $0[.gt] = ("$x", 0) }
+        $0[.d] { $0[.gte] = ("$x", 0) }
+        $0[.e] { $0[.lt] = ("$x", 0) }
+        $0[.f] { $0[.lte] = ("$x", 0) }
+        $0[.g] { $0[.ne] = ("$x", 0) }
     }
-    let _:BSON.Document = .init(BSON.Key.self)
+
+    let _:Mongo.SetDocument<Alphabet> = .init
     {
-        $0["_"] = .expr
-        {
-            $0[.and] = ("$x", true)
-        }
-        $0["_"] = .expr
+        $0[.a]  { $0[.and] = ("$x", true) }
+        $0[.b]
         {
             $0[.or]
             {
                 $0
                 {
-                    $0[.and] = ("$x", .expr
-                    {
-                        $0[.eq] = ("$y", 5)
-                    })
+                    $0[.and] = ("$x", .expr { $0[.eq] = ("$y", 5) })
                 }
             }
         }
-        $0["_"] = .expr
-        {
-            $0[.eq] = ("$x", 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.gt] = ("$x", 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.gte] = ("$x", 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.lt] = ("$x", 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.lte] = ("$x", 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.ne] = ("$x", 0)
-        }
+        $0[.c] { $0[.eq] = ("$x", 0) }
+        $0[.d] { $0[.gte] = ("$x", 0) }
+        $0[.e] { $0[.lt] = ("$x", 0) }
+        $0[.f] { $0[.lte] = ("$x", 0) }
+        $0[.g] { $0[.ne] = ("$x", 0) }
     }
-    let _:BSON.Document = .init(BSON.Key.self)
+
+    let _:Mongo.SetDocument<Alphabet> = .init
     {
-        $0["_"] = .expr
-        {
-            $0[.element] = (of: "$field", at: 0)
-        }
-        $0["_"] = .expr
-        {
-            $0[.arrayToObject] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.concatArrays] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.concatArrays] = ("$field", [] as [Never])
-        }
-        $0["_"] = .expr
+        $0[.a] { $0[.element] = (of: "$field", at: 0) }
+        $0[.b] { $0[.arrayToObject] = "$field" }
+        $0[.c] { $0[.concatArrays] = "$field" }
+        $0[.d] { $0[.concatArrays] = ("$field", [] as [Never]) }
+        $0[.e]
         {
             $0[.filter] = .let("x")
             {
                 $0[.input] = [0, 1, 2]
-                $0[.cond] = .expr
-                {
-                    $0[.gt] = ("$$x", 0)
-                }
+                $0[.cond] = .expr { $0[.gt] = ("$$x", 0) }
                 $0[.limit] = 10
             }
         }
-        $0["_"] = .expr
-        {
-            $0[.first] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.first] = (5, of: "$field")
-        }
-        $0["_"] = .expr
-        {
-            $0[.in] = ("$field", in: [4, 5, 6])
-        }
-        $0["_"] = .expr
-        {
-            $0[.elementIndex] = (in: "$field", of: 5.5, from: 0, to: nil as Never?)
-        }
-        $0["_"] = .expr
-        {
-            $0[.elementIndex] = (in: "$field", of: 5.5)
-        }
-        $0["_"] = .expr
-        {
-            $0[.isArray] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.last] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.last] = (5, of: "$field")
-        }
-        $0["_"] = .expr
+        $0[.f] { $0[.first] = "$field" }
+        $0[.g] { $0[.first] = (5, of: "$field") }
+        $0[.h] { $0[.in] = ("$field", in: [4, 5, 6]) }
+        $0[.i] { $0[.elementIndex] = (in: "$field", of: 5.5, from: 0, to: nil as Never?) }
+        $0[.j] { $0[.elementIndex] = (in: "$field", of: 5.5) }
+        $0[.k] { $0[.isArray] = "$field" }
+        $0[.l] { $0[.last] = "$field" }
+        $0[.m] { $0[.last] = (5, of: "$field") }
+        $0[.n]
         {
             $0[.map] = .let("x")
             {
                 $0[.input] = [0, 1, 2]
-                $0[.in] = .expr
-                {
-                    $0[.add] = ("$$x", 1)
-                }
+                $0[.in] = .expr { $0[.add] = ("$$x", 1) }
             }
         }
-        $0["_"] = .expr
-        {
-            $0[.max] = (5, of: "$field")
-        }
-        $0["_"] = .expr
-        {
-            $0[.min] = (5, of: "$field")
-        }
-        $0["_"] = .expr
-        {
-            $0[.not] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.objectToArray] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.range] = (from: "$start", to: "$end", by: 2)
-        }
-        $0["_"] = .expr
-        {
-            $0[.range] = (from: "$start", to: "$end")
-        }
-        $0["_"] = .expr
+        $0[.o] { $0[.max] = (5, of: "$field") }
+        $0[.p] { $0[.min] = (5, of: "$field") }
+        $0[.q] { $0[.not] = "$field" }
+        $0[.r] { $0[.objectToArray] = "$field" }
+        $0[.s] { $0[.range] = (from: "$start", to: "$end", by: 2) }
+        $0[.t] { $0[.range] = (from: "$start", to: "$end") }
+        $0[.u]
         {
             $0[.reduce] = .init
             {
                 $0[.input] = [0, 1, 2]
                 $0[.initialValue] = 0
-                $0[.in] = .expr
-                {
-                    $0[.add] = ("$$value", "$$this")
-                }
+                $0[.in] = .expr { $0[.add] = ("$$value", "$$this") }
             }
         }
-        $0["_"] = .expr
-        {
-            $0[.reverseArray] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.size] = "$field"
-        }
-        $0["_"] = .expr
-        {
-            $0[.slice] = ("$field", distance: -5)
-        }
-        $0["_"] = .expr
+        $0[.v] { $0[.reverseArray] = "$field" }
+        $0[.w] { $0[.size] = "$field" }
+        $0[.x] { $0[.slice] = ("$field", distance: -5) }
+        $0[.y] { $0[.slice] = ("$field", at: -2, distance: 1) }
+    }
+
+    let _:Mongo.SetDocument<Alphabet> = .init
+    {
+        $0[.a]
         {
-            $0[.slice] = ("$field", at: -2, distance: 1)
+            $0[.sortArray] = .init
+            {
+                $0[.input] = "$field"
+                $0[.by, using: Mongo.AnyKeyPath.self]
+                {
+                    $0["x"] = (+)
+                    $0["y"] = (-)
+                }
+            }
         }
-        $0["_"] = .expr
+
+        $0[.b]
         {
             $0[.sortArray] = .init
             {
@@ -375,7 +204,7 @@ func ExampleExpressions()
                 }
             }
         }
-        $0["_"] = .expr
+        $0[.c]
         {
             $0[.zip] = .init
             {
@@ -383,7 +212,7 @@ func ExampleExpressions()
                 $0[.defaults] = [0, 0]
             }
         }
-        $0["_"] = .expr
+        $0[.d]
         {
             $0[.zip] = .init
             {
@@ -391,7 +220,7 @@ func ExampleExpressions()
                 $0[.defaults] = [0, 0]
             }
         }
-        $0["_"] = .expr
+        $0[.e]
         {
             $0[.zip] = .init
             {
@@ -405,4 +234,3 @@ func ExampleExpressions()
         }
     }
 }
-