diff --git a/lib/6to5/transformation/transform.js b/lib/6to5/transformation/transform.js
index 123f52b6fb..6663a61697 100644
--- a/lib/6to5/transformation/transform.js
+++ b/lib/6to5/transformation/transform.js
@@ -3,6 +3,7 @@
 module.exports = transform;
 
 var Transformer = require("./transformer");
+var object      = require("../helpers/object");
 var File        = require("../file");
 var util        = require("../util");
 var _           = require("lodash");
@@ -24,7 +25,7 @@ transform.fromAst = function (ast, code, opts) {
 transform._ensureTransformerNames = function (type, keys) {
   for (var i = 0; i < keys.length; i++) {
     var key = keys[i];
-    if (!_.has(transform.transformers, key)) {
+    if (!transform.transformers[key]) {
       throw new ReferenceError(
         "Unknown transformer " + key + " specified in " + type + " - " +
         "transformer key names have been changed in 3.0.0 see " +
@@ -35,7 +36,7 @@ transform._ensureTransformerNames = function (type, keys) {
   }
 };
 
-transform.transformers = {};
+transform.transformers = object();
 
 transform.moduleFormatters = {
   common: require("./modules/common"),
@@ -46,18 +47,20 @@ transform.moduleFormatters = {
 };
 
 _.each({
-  "spec.noForInOfAssignment":           require("./transformers/spec/no-for-in-of-assignment"),
-  "spec.setters":                       require("./transformers/spec/setters"),
+  useStrict:                            require("./transformers/other/use-strict"),
+
+  "validation.undeclaredVariableCheck": require("./transformers/validation/undeclared-variable-check"),
+  "validation.noForInOfAssignment":     require("./transformers/validation/no-for-in-of-assignment"),
+  "validation.setters":                 require("./transformers/validation/setters"),
   "spec.blockScopedFunctions":          require("./transformers/spec/block-scoped-functions"),
-  "spec.illegalTopLevelThis":           require("./transformers/spec/illegal-top-level-this"),
 
   "playground.malletOperator":          require("./transformers/playground/mallet-operator"),
   "playground.methodBinding":           require("./transformers/playground/method-binding"),
   "playground.memoizationOperator":     require("./transformers/playground/memoization-operator"),
   "playground.objectGetterMemoization": require("./transformers/playground/object-getter-memoization"),
 
-  "optional.asyncToGenerator":        require("./transformers/optional/async-to-generator"),
-  "optional.bluebirdCoroutines":      require("./transformers/optional/bluebird-coroutines"),
+  "misc.asyncToGenerator":   require("./transformers/misc/async-to-generator"),
+  "misc.bluebirdCoroutines": require("./transformers/misc/bluebird-coroutines"),
 
   react:                              require("./transformers/other/react"),
 
@@ -96,9 +99,8 @@ _.each({
   "es6.blockScoping":                 require("./transformers/es6/block-scoping"),
 
   // needs to be after `es6.blockScoping` due to needing `letReferences` set on blocks
-  "optional.blockScopingTDZ":         require("./transformers/optional/block-scoping-tdz"),
+  "es6.blockScopingTDZ":              require("./transformers/es6/block-scoping-tdz"),
 
-  // needs to before `forOf` because otherwise regenerator wont be able to explode them
   // needs to be after block scoping since regenerator doesn't support it
   regenerator:                        require("./transformers/other/regenerator"),
 
@@ -110,25 +112,22 @@ _.each({
   // needs to be after `regenerator` due to needing `regeneratorRuntime` references
   // needs to be after `es6.forOf` due to needing `Symbol.iterator` references
   // needs to be before `es6.modules` due to dynamic imports
-  "optional.selfContained":           require("./transformers/optional/self-contained"),
+  "misc.selfContained":               require("./transformers/misc/self-contained"),
 
   _blockHoist:                        require("./transformers/_block-hoist"),
 
-  "optional.protoToAssign":           require("./transformers/optional/proto-to-assign"),
+  "spec.protoToAssign":               require("./transformers/spec/proto-to-assign"),
 
   _declarations:                      require("./transformers/_declarations"),
 
-  useStrict:                          require("./transformers/other/use-strict"),
-
   _aliasFunctions:                    require("./transformers/_alias-functions"),
   _moduleFormatter:                   require("./transformers/_module-formatter"),
 
-  "optional.typeofSymbol":            require("./transformers/optional/typeof-symbol"),
-  "optional.undefinedToVoid":         require("./transformers/optional/undefined-to-void"),
-  "optional.undeclaredVariableCheck": require("./transformers/optional/undeclared-variable-check"),
+  "spec.typeofSymbol":    require("./transformers/spec/typeof-symbol"),
+  "spec.undefinedToVoid": require("./transformers/spec/undefined-to-void"),
 
-  "spec.propertyLiterals":            require("./transformers/spec/property-literals"),
-  "spec.memberExpressionLiterals":    require("./transformers/spec/member-expression-literals")
+  "minification.propertyLiterals":         require("./transformers/minification/property-literals"),
+  "minification.memberExpressionLiterals": require("./transformers/minification/member-expression-literals")
 }, function (transformer, key) {
   transform.transformers[key] = new Transformer(key, transformer);
 });
diff --git a/lib/6to5/transformation/transformers/spec/member-expression-literals.js b/lib/6to5/transformation/transformers/minification/member-expression-literals.js
similarity index 86%
rename from lib/6to5/transformation/transformers/spec/member-expression-literals.js
rename to lib/6to5/transformation/transformers/minification/member-expression-literals.js
index 7b97bed4be..c360f560fb 100644
--- a/lib/6to5/transformation/transformers/spec/member-expression-literals.js
+++ b/lib/6to5/transformation/transformers/minification/member-expression-literals.js
@@ -5,10 +5,11 @@ var t = require("../../../types");
 exports.MemberExpression = function (node) {
   var prop = node.property;
   if (node.computed && t.isLiteral(prop) && t.isValidIdentifier(prop.value)) {
-    // computed literal that is a valid identifier
+    // foo["bar"] => foo.bar
     node.property = t.identifier(prop.value);
     node.computed = false;
   } else if (!node.computed && t.isIdentifier(prop) && !t.isValidIdentifier(prop.name)) {
+    // foo.default -> foo["default"]
     node.property = t.literal(prop.name);
     node.computed = true;
   }
diff --git a/lib/6to5/transformation/transformers/spec/property-literals.js b/lib/6to5/transformation/transformers/minification/property-literals.js
similarity index 80%
rename from lib/6to5/transformation/transformers/spec/property-literals.js
rename to lib/6to5/transformation/transformers/minification/property-literals.js
index b83882bac7..862c8eea94 100644
--- a/lib/6to5/transformation/transformers/spec/property-literals.js
+++ b/lib/6to5/transformation/transformers/minification/property-literals.js
@@ -5,11 +5,11 @@ var t = require("../../../types");
 exports.Property = function (node) {
   var key = node.key;
   if (t.isLiteral(key) && t.isValidIdentifier(key.value)) {
-    // property key is a literal but a valid identifier
+    // "foo": "bar" -> foo: "bar"
     node.key = t.identifier(key.value);
     node.computed = false;
   } else if (!node.computed && t.isIdentifier(key) && !t.isValidIdentifier(key.name)) {
-    // property key is a keyword
+    // default: "bar" -> "default": "bar"
     node.key = t.literal(key.name);
   }
 };
diff --git a/lib/6to5/transformation/transformers/optional/async-to-generator.js b/lib/6to5/transformation/transformers/misc/async-to-generator.js
similarity index 100%
rename from lib/6to5/transformation/transformers/optional/async-to-generator.js
rename to lib/6to5/transformation/transformers/misc/async-to-generator.js
diff --git a/lib/6to5/transformation/transformers/optional/bluebird-coroutines.js b/lib/6to5/transformation/transformers/misc/bluebird-coroutines.js
similarity index 100%
rename from lib/6to5/transformation/transformers/optional/bluebird-coroutines.js
rename to lib/6to5/transformation/transformers/misc/bluebird-coroutines.js
diff --git a/lib/6to5/transformation/transformers/optional/self-contained.js b/lib/6to5/transformation/transformers/misc/self-contained.js
similarity index 100%
rename from lib/6to5/transformation/transformers/optional/self-contained.js
rename to lib/6to5/transformation/transformers/misc/self-contained.js
diff --git a/lib/6to5/transformation/transformers/optional/block-scoping-tdz.js b/lib/6to5/transformation/transformers/optional/block-scoping-tdz.js
deleted file mode 100644
index b97f49ebb0..0000000000
--- a/lib/6to5/transformation/transformers/optional/block-scoping-tdz.js
+++ /dev/null
@@ -1,48 +0,0 @@
-var traverse = require("../../../traverse");
-var t        = require("../../../types");
-
-var visitor = {
-  enter: function (node, parent, scope, context, state) {
-    if (!t.isReferencedIdentifier(node, parent)) return;
-
-    var declared = state.letRefs[node.name];
-    if (!declared) return;
-
-    // declared node is different in this scope
-    if (scope.get(node.name, true) !== declared) return;
-
-    var declaredLoc  = declared.loc;
-    var referenceLoc = node.loc;
-
-    if (!declaredLoc || !referenceLoc) return;
-
-    // does this reference appear on a line before the declaration?
-    var before = referenceLoc.start.line < declaredLoc.start.line;
-
-    if (referenceLoc.start.line === declaredLoc.start.line) {
-      // this reference appears on the same line
-      // check it appears before the declaration
-      before = referenceLoc.start.col < declaredLoc.start.col;
-    }
-
-    if (before) {
-      throw state.file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
-    }
-  }
-};
-
-exports.optional = true;
-
-exports.Loop =
-exports.Program =
-exports.BlockStatement = function (node, parent, scope, context, file) {
-  var letRefs = node._letReferences;
-  if (!letRefs) return;
-
-  var state = {
-    letRefs: letRefs,
-    file:    file
-  };
-
-  traverse(node, visitor, scope, state);
-};
diff --git a/lib/6to5/transformation/transformers/other/react.js b/lib/6to5/transformation/transformers/other/react.js
index 9482f7e633..4059af0fc7 100644
--- a/lib/6to5/transformation/transformers/other/react.js
+++ b/lib/6to5/transformation/transformers/other/react.js
@@ -7,7 +7,6 @@
 
 var esutils = require("esutils");
 var t       = require("../../../types");
-var _       = require("lodash");
 
 exports.JSXIdentifier = function (node) {
   if (esutils.keyword.isIdentifierName(node.name)) {
@@ -148,7 +147,7 @@ exports.JSXElement = {
     for (var i = 0; i < node.children.length; i++) {
       var child = node.children[i];
 
-      if (t.isLiteral(child) && _.isString(child.value)) {
+      if (t.isLiteral(child) && typeof child.value === "string") {
         cleanJSXElementLiteralChild(child, callExpr.arguments);
         continue;
       } else if (t.isJSXEmptyExpression(child)) {
diff --git a/lib/6to5/transformation/transformers/other/use-strict.js b/lib/6to5/transformation/transformers/other/use-strict.js
index 5a06b90d7a..2b8251a41b 100644
--- a/lib/6to5/transformation/transformers/other/use-strict.js
+++ b/lib/6to5/transformation/transformers/other/use-strict.js
@@ -10,3 +10,12 @@ exports.ast = {
     }
   }
 };
+
+exports.FunctionDeclaration =
+exports.FunctionExpression = function (node, parent, scope, context) {
+  context.skip();
+};
+
+exports.ThisExpression = function (node, parent, scope, context, file) {
+  throw file.errorWithNode(node, "Top level `this` is not allowed", ReferenceError);
+};
diff --git a/lib/6to5/transformation/transformers/spec/illegal-top-level-this.js b/lib/6to5/transformation/transformers/spec/illegal-top-level-this.js
deleted file mode 100644
index e1edc90c31..0000000000
--- a/lib/6to5/transformation/transformers/spec/illegal-top-level-this.js
+++ /dev/null
@@ -1,8 +0,0 @@
-exports.FunctionDeclaration =
-exports.FunctionExpression = function (node, parent, scope, context) {
-  context.skip();
-};
-
-exports.ThisExpression = function (node, parent, scope, context, file) {
-  throw file.errorWithNode(node, "Top level `this` is not allowed", ReferenceError);
-};
diff --git a/lib/6to5/transformation/transformers/optional/proto-to-assign.js b/lib/6to5/transformation/transformers/spec/proto-to-assign.js
similarity index 100%
rename from lib/6to5/transformation/transformers/optional/proto-to-assign.js
rename to lib/6to5/transformation/transformers/spec/proto-to-assign.js
diff --git a/lib/6to5/transformation/transformers/optional/typeof-symbol.js b/lib/6to5/transformation/transformers/spec/typeof-symbol.js
similarity index 100%
rename from lib/6to5/transformation/transformers/optional/typeof-symbol.js
rename to lib/6to5/transformation/transformers/spec/typeof-symbol.js
diff --git a/lib/6to5/transformation/transformers/optional/undefined-to-void.js b/lib/6to5/transformation/transformers/spec/undefined-to-void.js
similarity index 100%
rename from lib/6to5/transformation/transformers/optional/undefined-to-void.js
rename to lib/6to5/transformation/transformers/spec/undefined-to-void.js
diff --git a/lib/6to5/transformation/transformers/spec/no-for-in-of-assignment.js b/lib/6to5/transformation/transformers/validation/no-for-in-of-assignment.js
similarity index 100%
rename from lib/6to5/transformation/transformers/spec/no-for-in-of-assignment.js
rename to lib/6to5/transformation/transformers/validation/no-for-in-of-assignment.js
diff --git a/lib/6to5/transformation/transformers/spec/setters.js b/lib/6to5/transformation/transformers/validation/setters.js
similarity index 100%
rename from lib/6to5/transformation/transformers/spec/setters.js
rename to lib/6to5/transformation/transformers/validation/setters.js
diff --git a/lib/6to5/transformation/transformers/optional/undeclared-variable-check.js b/lib/6to5/transformation/transformers/validation/undeclared-variable-check.js
similarity index 100%
rename from lib/6to5/transformation/transformers/optional/undeclared-variable-check.js
rename to lib/6to5/transformation/transformers/validation/undeclared-variable-check.js
diff --git a/test/fixtures/transformation/spec/member-expression-literals/actual.js b/test/fixtures/transformation/minification/member-expression-literals/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec/member-expression-literals/actual.js
rename to test/fixtures/transformation/minification/member-expression-literals/actual.js
diff --git a/test/fixtures/transformation/spec/member-expression-literals/expected.js b/test/fixtures/transformation/minification/member-expression-literals/expected.js
similarity index 100%
rename from test/fixtures/transformation/spec/member-expression-literals/expected.js
rename to test/fixtures/transformation/minification/member-expression-literals/expected.js
diff --git a/test/fixtures/transformation/spec/property-literals/actual.js b/test/fixtures/transformation/minification/property-literals/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec/property-literals/actual.js
rename to test/fixtures/transformation/minification/property-literals/actual.js
diff --git a/test/fixtures/transformation/spec/property-literals/expected.js b/test/fixtures/transformation/minification/property-literals/expected.js
similarity index 100%
rename from test/fixtures/transformation/spec/property-literals/expected.js
rename to test/fixtures/transformation/minification/property-literals/expected.js
diff --git a/test/fixtures/transformation/optional-async-to-generator/expression/actual.js b/test/fixtures/transformation/misc-async-to-generator/expression/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-async-to-generator/expression/actual.js
rename to test/fixtures/transformation/misc-async-to-generator/expression/actual.js
diff --git a/test/fixtures/transformation/optional-async-to-generator/expression/expected.js b/test/fixtures/transformation/misc-async-to-generator/expression/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-async-to-generator/expression/expected.js
rename to test/fixtures/transformation/misc-async-to-generator/expression/expected.js
diff --git a/test/fixtures/transformation/misc-async-to-generator/options.json b/test/fixtures/transformation/misc-async-to-generator/options.json
new file mode 100644
index 0000000000..f5ac3882dd
--- /dev/null
+++ b/test/fixtures/transformation/misc-async-to-generator/options.json
@@ -0,0 +1,4 @@
+{
+  "noCheckAst": true,
+  "optional": ["misc.asyncToGenerator"]
+}
diff --git a/test/fixtures/transformation/optional-async-to-generator/statement/actual.js b/test/fixtures/transformation/misc-async-to-generator/statement/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-async-to-generator/statement/actual.js
rename to test/fixtures/transformation/misc-async-to-generator/statement/actual.js
diff --git a/test/fixtures/transformation/optional-async-to-generator/statement/expected.js b/test/fixtures/transformation/misc-async-to-generator/statement/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-async-to-generator/statement/expected.js
rename to test/fixtures/transformation/misc-async-to-generator/statement/expected.js
diff --git a/test/fixtures/transformation/optional-bluebird-coroutines/expression/actual.js b/test/fixtures/transformation/misc-bluebird-coroutines/expression/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-bluebird-coroutines/expression/actual.js
rename to test/fixtures/transformation/misc-bluebird-coroutines/expression/actual.js
diff --git a/test/fixtures/transformation/optional-bluebird-coroutines/expression/expected.js b/test/fixtures/transformation/misc-bluebird-coroutines/expression/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-bluebird-coroutines/expression/expected.js
rename to test/fixtures/transformation/misc-bluebird-coroutines/expression/expected.js
diff --git a/test/fixtures/transformation/misc-bluebird-coroutines/options.json b/test/fixtures/transformation/misc-bluebird-coroutines/options.json
new file mode 100644
index 0000000000..5a66a3ffe6
--- /dev/null
+++ b/test/fixtures/transformation/misc-bluebird-coroutines/options.json
@@ -0,0 +1,4 @@
+{
+  "optional": ["misc.bluebirdCoroutines"],
+  "noCheckAst": true
+}
diff --git a/test/fixtures/transformation/optional-bluebird-coroutines/statement/actual.js b/test/fixtures/transformation/misc-bluebird-coroutines/statement/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-bluebird-coroutines/statement/actual.js
rename to test/fixtures/transformation/misc-bluebird-coroutines/statement/actual.js
diff --git a/test/fixtures/transformation/optional-bluebird-coroutines/statement/expected.js b/test/fixtures/transformation/misc-bluebird-coroutines/statement/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-bluebird-coroutines/statement/expected.js
rename to test/fixtures/transformation/misc-bluebird-coroutines/statement/expected.js
diff --git a/test/fixtures/transformation/optional-self-contained/aliased-constructors/actual.js b/test/fixtures/transformation/misc-self-contained/aliased-constructors/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/aliased-constructors/actual.js
rename to test/fixtures/transformation/misc-self-contained/aliased-constructors/actual.js
diff --git a/test/fixtures/transformation/optional-self-contained/aliased-constructors/expected.js b/test/fixtures/transformation/misc-self-contained/aliased-constructors/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/aliased-constructors/expected.js
rename to test/fixtures/transformation/misc-self-contained/aliased-constructors/expected.js
diff --git a/test/fixtures/transformation/optional-self-contained/es6-for-of/actual.js b/test/fixtures/transformation/misc-self-contained/es6-for-of/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/es6-for-of/actual.js
rename to test/fixtures/transformation/misc-self-contained/es6-for-of/actual.js
diff --git a/test/fixtures/transformation/optional-self-contained/es6-for-of/expected.js b/test/fixtures/transformation/misc-self-contained/es6-for-of/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/es6-for-of/expected.js
rename to test/fixtures/transformation/misc-self-contained/es6-for-of/expected.js
diff --git a/test/fixtures/transformation/optional-self-contained/es7-array-comprehensions/actual.js b/test/fixtures/transformation/misc-self-contained/es7-array-comprehensions/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/es7-array-comprehensions/actual.js
rename to test/fixtures/transformation/misc-self-contained/es7-array-comprehensions/actual.js
diff --git a/test/fixtures/transformation/optional-self-contained/es7-array-comprehensions/expected.js b/test/fixtures/transformation/misc-self-contained/es7-array-comprehensions/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/es7-array-comprehensions/expected.js
rename to test/fixtures/transformation/misc-self-contained/es7-array-comprehensions/expected.js
diff --git a/test/fixtures/transformation/optional-self-contained/full/actual.js b/test/fixtures/transformation/misc-self-contained/full/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/full/actual.js
rename to test/fixtures/transformation/misc-self-contained/full/actual.js
diff --git a/test/fixtures/transformation/optional-self-contained/full/expected.js b/test/fixtures/transformation/misc-self-contained/full/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/full/expected.js
rename to test/fixtures/transformation/misc-self-contained/full/expected.js
diff --git a/test/fixtures/transformation/misc-self-contained/options.json b/test/fixtures/transformation/misc-self-contained/options.json
new file mode 100644
index 0000000000..a28ebc7a9e
--- /dev/null
+++ b/test/fixtures/transformation/misc-self-contained/options.json
@@ -0,0 +1,4 @@
+{
+  "optional": ["misc.selfContained"],
+  "experimental": true
+}
diff --git a/test/fixtures/transformation/optional-self-contained/regenerator-runtime/actual.js b/test/fixtures/transformation/misc-self-contained/regenerator-runtime/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/regenerator-runtime/actual.js
rename to test/fixtures/transformation/misc-self-contained/regenerator-runtime/actual.js
diff --git a/test/fixtures/transformation/optional-self-contained/regenerator-runtime/expected.js b/test/fixtures/transformation/misc-self-contained/regenerator-runtime/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/regenerator-runtime/expected.js
rename to test/fixtures/transformation/misc-self-contained/regenerator-runtime/expected.js
diff --git a/test/fixtures/transformation/optional-self-contained/runtime-amd/actual.js b/test/fixtures/transformation/misc-self-contained/runtime-amd/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/runtime-amd/actual.js
rename to test/fixtures/transformation/misc-self-contained/runtime-amd/actual.js
diff --git a/test/fixtures/transformation/optional-self-contained/runtime-amd/expected.js b/test/fixtures/transformation/misc-self-contained/runtime-amd/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/runtime-amd/expected.js
rename to test/fixtures/transformation/misc-self-contained/runtime-amd/expected.js
diff --git a/test/fixtures/transformation/optional-self-contained/runtime-amd/options.json b/test/fixtures/transformation/misc-self-contained/runtime-amd/options.json
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/runtime-amd/options.json
rename to test/fixtures/transformation/misc-self-contained/runtime-amd/options.json
diff --git a/test/fixtures/transformation/optional-self-contained/runtime-commonjs/actual.js b/test/fixtures/transformation/misc-self-contained/runtime-commonjs/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/runtime-commonjs/actual.js
rename to test/fixtures/transformation/misc-self-contained/runtime-commonjs/actual.js
diff --git a/test/fixtures/transformation/optional-self-contained/runtime-commonjs/expected.js b/test/fixtures/transformation/misc-self-contained/runtime-commonjs/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-self-contained/runtime-commonjs/expected.js
rename to test/fixtures/transformation/misc-self-contained/runtime-commonjs/expected.js
diff --git a/test/fixtures/transformation/optional-async-to-generator/options.json b/test/fixtures/transformation/optional-async-to-generator/options.json
deleted file mode 100644
index 9dbdefeeb0..0000000000
--- a/test/fixtures/transformation/optional-async-to-generator/options.json
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  "noCheckAst": true,
-  "optional": ["asyncToGenerator"]
-}
diff --git a/test/fixtures/transformation/optional-bluebird-coroutines/options.json b/test/fixtures/transformation/optional-bluebird-coroutines/options.json
deleted file mode 100644
index beb0408342..0000000000
--- a/test/fixtures/transformation/optional-bluebird-coroutines/options.json
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  "optional": ["bluebirdCoroutines"],
-  "noCheckAst": true
-}
diff --git a/test/fixtures/transformation/optional-proto-to-assign/options.json b/test/fixtures/transformation/optional-proto-to-assign/options.json
deleted file mode 100644
index bff9598732..0000000000
--- a/test/fixtures/transformation/optional-proto-to-assign/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "optional": ["protoToAssign"]
-}
diff --git a/test/fixtures/transformation/optional-self-contained/options.json b/test/fixtures/transformation/optional-self-contained/options.json
deleted file mode 100644
index 079cf304ad..0000000000
--- a/test/fixtures/transformation/optional-self-contained/options.json
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  "optional": ["selfContained"],
-  "experimental": true
-}
diff --git a/test/fixtures/transformation/optional-typeof-symbol/options.json b/test/fixtures/transformation/optional-typeof-symbol/options.json
deleted file mode 100644
index 6e208aa132..0000000000
--- a/test/fixtures/transformation/optional-typeof-symbol/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "optional": ["typeofSymbol"]
-}
diff --git a/test/fixtures/transformation/optional-undeclared-variable-check/options.json b/test/fixtures/transformation/optional-undeclared-variable-check/options.json
deleted file mode 100644
index 535d39109b..0000000000
--- a/test/fixtures/transformation/optional-undeclared-variable-check/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "optional": ["undeclaredVariableCheck"]
-}
diff --git a/test/fixtures/transformation/optional-undefined-to-void/options.json b/test/fixtures/transformation/optional-undefined-to-void/options.json
deleted file mode 100644
index 951ad97b89..0000000000
--- a/test/fixtures/transformation/optional-undefined-to-void/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "optional": ["undefinedToVoid"]
-}
diff --git a/test/fixtures/transformation/optional-proto-to-assign/assignment-expression/actual.js b/test/fixtures/transformation/spec-proto-to-assign/assignment-expression/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-proto-to-assign/assignment-expression/actual.js
rename to test/fixtures/transformation/spec-proto-to-assign/assignment-expression/actual.js
diff --git a/test/fixtures/transformation/optional-proto-to-assign/assignment-expression/expected.js b/test/fixtures/transformation/spec-proto-to-assign/assignment-expression/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-proto-to-assign/assignment-expression/expected.js
rename to test/fixtures/transformation/spec-proto-to-assign/assignment-expression/expected.js
diff --git a/test/fixtures/transformation/optional-proto-to-assign/assignment-statement/actual.js b/test/fixtures/transformation/spec-proto-to-assign/assignment-statement/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-proto-to-assign/assignment-statement/actual.js
rename to test/fixtures/transformation/spec-proto-to-assign/assignment-statement/actual.js
diff --git a/test/fixtures/transformation/optional-proto-to-assign/assignment-statement/expected.js b/test/fixtures/transformation/spec-proto-to-assign/assignment-statement/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-proto-to-assign/assignment-statement/expected.js
rename to test/fixtures/transformation/spec-proto-to-assign/assignment-statement/expected.js
diff --git a/test/fixtures/transformation/optional-proto-to-assign/class/actual.js b/test/fixtures/transformation/spec-proto-to-assign/class/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-proto-to-assign/class/actual.js
rename to test/fixtures/transformation/spec-proto-to-assign/class/actual.js
diff --git a/test/fixtures/transformation/optional-proto-to-assign/class/expected.js b/test/fixtures/transformation/spec-proto-to-assign/class/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-proto-to-assign/class/expected.js
rename to test/fixtures/transformation/spec-proto-to-assign/class/expected.js
diff --git a/test/fixtures/transformation/optional-proto-to-assign/object-literal/actual.js b/test/fixtures/transformation/spec-proto-to-assign/object-literal/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-proto-to-assign/object-literal/actual.js
rename to test/fixtures/transformation/spec-proto-to-assign/object-literal/actual.js
diff --git a/test/fixtures/transformation/optional-proto-to-assign/object-literal/expected.js b/test/fixtures/transformation/spec-proto-to-assign/object-literal/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-proto-to-assign/object-literal/expected.js
rename to test/fixtures/transformation/spec-proto-to-assign/object-literal/expected.js
diff --git a/test/fixtures/transformation/spec-proto-to-assign/options.json b/test/fixtures/transformation/spec-proto-to-assign/options.json
new file mode 100644
index 0000000000..d9ea3ea443
--- /dev/null
+++ b/test/fixtures/transformation/spec-proto-to-assign/options.json
@@ -0,0 +1,3 @@
+{
+  "optional": ["spec.protoToAssign"]
+}
diff --git a/test/fixtures/transformation/optional-typeof-symbol/basic/actual.js b/test/fixtures/transformation/spec-typeof-symbol/basic/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-typeof-symbol/basic/actual.js
rename to test/fixtures/transformation/spec-typeof-symbol/basic/actual.js
diff --git a/test/fixtures/transformation/optional-typeof-symbol/basic/exec.js b/test/fixtures/transformation/spec-typeof-symbol/basic/exec.js
similarity index 100%
rename from test/fixtures/transformation/optional-typeof-symbol/basic/exec.js
rename to test/fixtures/transformation/spec-typeof-symbol/basic/exec.js
diff --git a/test/fixtures/transformation/optional-typeof-symbol/basic/expected.js b/test/fixtures/transformation/spec-typeof-symbol/basic/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-typeof-symbol/basic/expected.js
rename to test/fixtures/transformation/spec-typeof-symbol/basic/expected.js
diff --git a/test/fixtures/transformation/spec-typeof-symbol/options.json b/test/fixtures/transformation/spec-typeof-symbol/options.json
new file mode 100644
index 0000000000..9d920d3af0
--- /dev/null
+++ b/test/fixtures/transformation/spec-typeof-symbol/options.json
@@ -0,0 +1,3 @@
+{
+  "optional": ["spec.typeofSymbol"]
+}
diff --git a/test/fixtures/transformation/optional-undefined-to-void/basic/actual.js b/test/fixtures/transformation/spec-undefined-to-void/basic/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-undefined-to-void/basic/actual.js
rename to test/fixtures/transformation/spec-undefined-to-void/basic/actual.js
diff --git a/test/fixtures/transformation/optional-undefined-to-void/basic/expected.js b/test/fixtures/transformation/spec-undefined-to-void/basic/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-undefined-to-void/basic/expected.js
rename to test/fixtures/transformation/spec-undefined-to-void/basic/expected.js
diff --git a/test/fixtures/transformation/optional-undefined-to-void/member-expression/actual.js b/test/fixtures/transformation/spec-undefined-to-void/member-expression/actual.js
similarity index 100%
rename from test/fixtures/transformation/optional-undefined-to-void/member-expression/actual.js
rename to test/fixtures/transformation/spec-undefined-to-void/member-expression/actual.js
diff --git a/test/fixtures/transformation/optional-undefined-to-void/member-expression/expected.js b/test/fixtures/transformation/spec-undefined-to-void/member-expression/expected.js
similarity index 100%
rename from test/fixtures/transformation/optional-undefined-to-void/member-expression/expected.js
rename to test/fixtures/transformation/spec-undefined-to-void/member-expression/expected.js
diff --git a/test/fixtures/transformation/spec-undefined-to-void/options.json b/test/fixtures/transformation/spec-undefined-to-void/options.json
new file mode 100644
index 0000000000..d8a082be4c
--- /dev/null
+++ b/test/fixtures/transformation/spec-undefined-to-void/options.json
@@ -0,0 +1,3 @@
+{
+  "optional": ["spec.undefinedToVoid"]
+}
diff --git a/test/fixtures/transformation/spec-illegal-top-level-this/arrow-function/actual.js b/test/fixtures/transformation/use-strict/illegal-this-arrow-function/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec-illegal-top-level-this/arrow-function/actual.js
rename to test/fixtures/transformation/use-strict/illegal-this-arrow-function/actual.js
diff --git a/test/fixtures/transformation/spec-illegal-top-level-this/options.json b/test/fixtures/transformation/use-strict/illegal-this-arrow-function/options.json
similarity index 100%
rename from test/fixtures/transformation/spec-illegal-top-level-this/options.json
rename to test/fixtures/transformation/use-strict/illegal-this-arrow-function/options.json
diff --git a/test/fixtures/transformation/spec-illegal-top-level-this/root-call/actual.js b/test/fixtures/transformation/use-strict/illegal-this-root-call/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec-illegal-top-level-this/root-call/actual.js
rename to test/fixtures/transformation/use-strict/illegal-this-root-call/actual.js
diff --git a/test/fixtures/transformation/use-strict/illegal-this-root-call/options.json b/test/fixtures/transformation/use-strict/illegal-this-root-call/options.json
new file mode 100644
index 0000000000..c1e1e00456
--- /dev/null
+++ b/test/fixtures/transformation/use-strict/illegal-this-root-call/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "Top level `this` is not allowed"
+}
diff --git a/test/fixtures/transformation/spec-illegal-top-level-this/root-declaration/actual.js b/test/fixtures/transformation/use-strict/illegal-this-root-declaration/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec-illegal-top-level-this/root-declaration/actual.js
rename to test/fixtures/transformation/use-strict/illegal-this-root-declaration/actual.js
diff --git a/test/fixtures/transformation/use-strict/illegal-this-root-declaration/options.json b/test/fixtures/transformation/use-strict/illegal-this-root-declaration/options.json
new file mode 100644
index 0000000000..c1e1e00456
--- /dev/null
+++ b/test/fixtures/transformation/use-strict/illegal-this-root-declaration/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "Top level `this` is not allowed"
+}
diff --git a/test/fixtures/transformation/spec-illegal-top-level-this/root-reference/actual.js b/test/fixtures/transformation/use-strict/illegal-this-root-reference/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec-illegal-top-level-this/root-reference/actual.js
rename to test/fixtures/transformation/use-strict/illegal-this-root-reference/actual.js
diff --git a/test/fixtures/transformation/use-strict/illegal-this-root-reference/options.json b/test/fixtures/transformation/use-strict/illegal-this-root-reference/options.json
new file mode 100644
index 0000000000..c1e1e00456
--- /dev/null
+++ b/test/fixtures/transformation/use-strict/illegal-this-root-reference/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "Top level `this` is not allowed"
+}
diff --git a/test/fixtures/transformation/use-strict/add/actual.js b/test/fixtures/transformation/use-strict/use-strict-add/actual.js
similarity index 100%
rename from test/fixtures/transformation/use-strict/add/actual.js
rename to test/fixtures/transformation/use-strict/use-strict-add/actual.js
diff --git a/test/fixtures/transformation/use-strict/add/expected.js b/test/fixtures/transformation/use-strict/use-strict-add/expected.js
similarity index 100%
rename from test/fixtures/transformation/use-strict/add/expected.js
rename to test/fixtures/transformation/use-strict/use-strict-add/expected.js
diff --git a/test/fixtures/transformation/use-strict/exists/actual.js b/test/fixtures/transformation/use-strict/use-strict-exists/actual.js
similarity index 100%
rename from test/fixtures/transformation/use-strict/exists/actual.js
rename to test/fixtures/transformation/use-strict/use-strict-exists/actual.js
diff --git a/test/fixtures/transformation/use-strict/exists/expected.js b/test/fixtures/transformation/use-strict/use-strict-exists/expected.js
similarity index 100%
rename from test/fixtures/transformation/use-strict/exists/expected.js
rename to test/fixtures/transformation/use-strict/use-strict-exists/expected.js
diff --git a/test/fixtures/transformation/spec-setters/class-no-args/actual.js b/test/fixtures/transformation/validation-setters/class-no-args/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec-setters/class-no-args/actual.js
rename to test/fixtures/transformation/validation-setters/class-no-args/actual.js
diff --git a/test/fixtures/transformation/spec-setters/class-two-args/actual.js b/test/fixtures/transformation/validation-setters/class-two-args/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec-setters/class-two-args/actual.js
rename to test/fixtures/transformation/validation-setters/class-two-args/actual.js
diff --git a/test/fixtures/transformation/spec-setters/object-no-args/actual.js b/test/fixtures/transformation/validation-setters/object-no-args/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec-setters/object-no-args/actual.js
rename to test/fixtures/transformation/validation-setters/object-no-args/actual.js
diff --git a/test/fixtures/transformation/spec-setters/object-two-args/actual.js b/test/fixtures/transformation/validation-setters/object-two-args/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec-setters/object-two-args/actual.js
rename to test/fixtures/transformation/validation-setters/object-two-args/actual.js
diff --git a/test/fixtures/transformation/spec-setters/options.json b/test/fixtures/transformation/validation-setters/options.json
similarity index 100%
rename from test/fixtures/transformation/spec-setters/options.json
rename to test/fixtures/transformation/validation-setters/options.json
diff --git a/test/fixtures/transformation/optional-undeclared-variable-check/declared/exec.js b/test/fixtures/transformation/validation-undeclared-variable-check/declared/exec.js
similarity index 100%
rename from test/fixtures/transformation/optional-undeclared-variable-check/declared/exec.js
rename to test/fixtures/transformation/validation-undeclared-variable-check/declared/exec.js
diff --git a/test/fixtures/transformation/validation-undeclared-variable-check/options.json b/test/fixtures/transformation/validation-undeclared-variable-check/options.json
new file mode 100644
index 0000000000..577e93ea79
--- /dev/null
+++ b/test/fixtures/transformation/validation-undeclared-variable-check/options.json
@@ -0,0 +1,3 @@
+{
+  "optional": ["validation.undeclaredVariableCheck"]
+}
diff --git a/test/fixtures/transformation/optional-undeclared-variable-check/undeclared/exec.js b/test/fixtures/transformation/validation-undeclared-variable-check/undeclared/exec.js
similarity index 100%
rename from test/fixtures/transformation/optional-undeclared-variable-check/undeclared/exec.js
rename to test/fixtures/transformation/validation-undeclared-variable-check/undeclared/exec.js
diff --git a/test/fixtures/transformation/optional-undeclared-variable-check/undeclared/options.json b/test/fixtures/transformation/validation-undeclared-variable-check/undeclared/options.json
similarity index 100%
rename from test/fixtures/transformation/optional-undeclared-variable-check/undeclared/options.json
rename to test/fixtures/transformation/validation-undeclared-variable-check/undeclared/options.json
diff --git a/test/fixtures/transformation/spec/for-in-assignment/actual.js b/test/fixtures/transformation/validation/for-in-assignment/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec/for-in-assignment/actual.js
rename to test/fixtures/transformation/validation/for-in-assignment/actual.js
diff --git a/test/fixtures/transformation/spec/for-in-assignment/options.json b/test/fixtures/transformation/validation/for-in-assignment/options.json
similarity index 100%
rename from test/fixtures/transformation/spec/for-in-assignment/options.json
rename to test/fixtures/transformation/validation/for-in-assignment/options.json
diff --git a/test/fixtures/transformation/spec/for-of-assignment/actual.js b/test/fixtures/transformation/validation/for-of-assignment/actual.js
similarity index 100%
rename from test/fixtures/transformation/spec/for-of-assignment/actual.js
rename to test/fixtures/transformation/validation/for-of-assignment/actual.js
diff --git a/test/fixtures/transformation/spec/for-of-assignment/options.json b/test/fixtures/transformation/validation/for-of-assignment/options.json
similarity index 100%
rename from test/fixtures/transformation/spec/for-of-assignment/options.json
rename to test/fixtures/transformation/validation/for-of-assignment/options.json