docs(compile/notassign): description for compile/notassign error

Closes #3459

docs/content/error/compile/noass.ngdoc

@@ -1,4 +0,0 @@
-@ngdoc error
-@name $compile:noass
-@fullName Non-Assignable Expression
-@description

docs/content/error/compile/nonassign.ngdoc

@@ -0,0 +1,36 @@
+@ngdoc error
+@name $compile:nonassign
+@fullName Non-Assignable Expression
+@description
+
+This error occurs when a directive defines an isolate scope property that support two-way data-binding (using the `=` mode in the {@link guide/directive#directivedefinitionobject  directive definition}) but the directive is used with an expression that is not-assignable.
+
+In order for the two-way data-binding to work, it must be possible to write new values back into the path defined with the expression.
+
+For example, given a directive:
+
+```
+myModule.directive('myDirective', function factory() {
+  return {
+    ...
+    scope: {
+      'bind': '=localValue'
+    }
+    ...
+  }
+});
+```
+
+Following are invalid uses of this directive:
+```
+<my-directive bind="1+2">    <!-- ERROR because `1+2=localValue` is an invalid statement -->
+<my-directive bind="myFn()"> <!-- ERROR because `myFn()=localValue` is an invalid statement -->
+```
+
+
+To resolve this error, always use path expressions with scope properties that are two-way data-bound:
+```
+<my-directive bind="some.property">
+<my-directive bind="some[3]['property']">
+```
+

src/ng/compile.js

@@ -978,7 +978,7 @@ function $CompileProvider($provide) {
                 parentSet = parentGet.assign || function() {
                   // reset the change, or we will throw this exception on every $digest
                   lastValue = scope[scopeName] = parentGet(parentScope);
-                  throw $compileMinErr('noass', "Expression '{0}' used with directive '{1}' is non-assignable!",
+                  throw $compileMinErr('nonassign', "Expression '{0}' used with directive '{1}' is non-assignable!",
                       attrs[attrName], newIsolateScopeDirective.name);
                 };
                 lastValue = scope[scopeName] = parentGet(parentScope);

test/ng/compileSpec.js

@@ -2110,7 +2110,7 @@ describe('$compile', function() {
 
         componentScope.ref = 'ignore me';
         expect($rootScope.$apply).
-            toThrow("[$compile:noass] Expression ''hello ' + name' used with directive 'myComponent' is non-assignable!");
+            toThrow("[$compile:nonassign] Expression ''hello ' + name' used with directive 'myComponent' is non-assignable!");
         expect(componentScope.ref).toBe('hello world');
         // reset since the exception was rethrown which prevented phase clearing
         $rootScope.$$phase = null;
@@ -3240,7 +3240,7 @@ describe('$compile', function() {
           };
         });
       });
-      inject(function($compile, $rootScope) {
+      inject(function($compile) {
         expect(function() {
           element = $compile(
               '<div>' +