diff --git a/lib/specs/spec_0_3.js b/lib/specs/spec_0_3.js
index 11a0257..371a412 100644
--- a/lib/specs/spec_0_3.js
+++ b/lib/specs/spec_0_3.js
@@ -2,8 +2,11 @@ const uuid  = require("uuid/v4");
 const empty = require("is-empty");
 const Ajv   = require("ajv");
 
-// Reserved attributes names
-const reserved = {
+const {
+  equalsOrThrow
+} = require("../utils/fun.js");
+
+const RESERVED_ATTRIBUTES = {
   type: "type",
   specversion: "specversion",
   source: "source",
@@ -16,13 +19,16 @@ const reserved = {
   data: "data"
 };
 
+const SUPPORTED_CONTENT_ENCODING = [];
+SUPPORTED_CONTENT_ENCODING.push("base64");
+
 const schema = require("../../ext/spec_0_3.json");
 
 const ajv = new Ajv({
   extendRefs: true
 });
 
-const validate = ajv.compile(schema);
+const isValidAgainstSchema = ajv.compile(schema);
 
 function Spec03(_caller){
   this.payload = {
@@ -67,14 +73,31 @@ function Spec03(_caller){
  * Check the spec constraints
  */
 Spec03.prototype.check = function(ce){
-  var toCheck = ce;
-  if(!toCheck) {
-    toCheck = this.payload;
-  }
-  var valid = validate(toCheck);
+  var toCheck = (!ce ? this.payload : ce);
+
+  var valid = isValidAgainstSchema(toCheck);
+
+  Array.of(toCheck)
+    .filter((tc) => (typeof tc.data) !== 'string')
+    .filter((tc) => tc["datacontentencoding"])
+    .forEach((tc) => {
+      throw {message: "invalid payload", errors: [
+        "Use 'datacontentencoding' when 'data' is a string"
+      ]};
+    });
+
+  Array.of(toCheck)
+    .filter((tc) => tc["datacontentencoding"])
+    .map((tc) => tc["datacontentencoding"].toLocaleLowerCase("en-US"))
+    .filter((dce) => !SUPPORTED_CONTENT_ENCODING.includes(dce))
+    .forEach((dce) => {
+      throw {message: "invalid payload", errors: [
+        "Unsupported content encoding: " + dce
+      ]};
+    })
 
   if(!valid) {
-    throw {message: "invalid payload", errors: validate.errors};
+    throw {message: "invalid payload", errors: isValidAgainstSchema.errors};
   }
 };
 
@@ -173,7 +196,7 @@ Spec03.prototype.getData = function() {
 };
 
 Spec03.prototype.addExtension = function(key, value){
-  if(!reserved.hasOwnProperty(key)){
+  if(!RESERVED_ATTRIBUTES.hasOwnProperty(key)){
     this.payload[key] = value;
   } else {
     throw {message: "Reserved attribute name: '" + key + "'"};
diff --git a/lib/utils/fun.js b/lib/utils/fun.js
index 03abded..5534889 100644
--- a/lib/utils/fun.js
+++ b/lib/utils/fun.js
@@ -3,6 +3,11 @@ const isString = (v) => (typeof v) === "string";
 const isObject = (v) => (typeof v) === "object";
 const isDefined = (v) => v && (typeof v) != "undefined";
 
+const isStringOrThrow = (v, t) =>
+  (isString(v)
+    ? true
+    : (() => {throw t;})());
+
 const isDefinedOrThrow = (v, t) =>
   (isDefined(v)
     ?  () => true
@@ -15,11 +20,19 @@ const isStringOrObjectOrThrow = (v, t) =>
             ? true
             : (() => {throw t;})());
 
+const equalsOrThrow = (v1, v2, t) =>
+  (v1 === v2
+    ? true
+    : (() => {throw t;})());
+
 module.exports = {
   isString,
+  isStringOrThrow,
   isObject,
   isDefined,
 
   isDefinedOrThrow,
-  isStringOrObjectOrThrow
+  isStringOrObjectOrThrow,
+
+  equalsOrThrow
 };
diff --git a/test/fun_tests.js b/test/fun_tests.js
new file mode 100644
index 0000000..aa4fdb9
--- /dev/null
+++ b/test/fun_tests.js
@@ -0,0 +1,32 @@
+const expect = require("chai").expect;
+const fun = require("../lib/utils/fun.js");
+
+describe("Functional approach", () => {
+  describe("isStringOrThrow", () => {
+    it("should throw when is not a string", () => {
+      expect(fun.isStringOrThrow.bind(fun, 3.6, {message: "works!"}))
+        .to
+        .throw("works!");
+    });
+
+    it("should return true when is a string", () => {
+      expect(fun.isStringOrThrow("cool", {message: "not throws!"}))
+        .to
+        .equals(true);
+    });
+  });
+
+  describe("equalsOrThrow", () => {
+    it("should throw when they are not equals", () => {
+      expect(fun.equalsOrThrow.bind(fun, "z", "a", {message: "works!"}))
+        .to
+        .throw("works!");
+    });
+
+    it("should return true when they are equals", () => {
+      expect(fun.equalsOrThrow("z", "z", {message: "not throws!"}))
+        .to
+        .equals(true);
+    });
+  });
+});
diff --git a/test/spec_0_3_tests.js b/test/spec_0_3_tests.js
index a4fe982..51c3863 100644
--- a/test/spec_0_3_tests.js
+++ b/test/spec_0_3_tests.js
@@ -21,7 +21,6 @@ var cloudevent =
     .id(id)
     .source(source)
     .type(type)
-    .dataContentEncoding(dataContentEncoding)
     .dataContentType(dataContentType)
     .schemaurl(schemaurl)
     .subject(subject)
@@ -50,7 +49,10 @@ describe("CloudEvents Spec v0.3", () => {
 
   describe("OPTIONAL Attributes", () => {
     it("Should have 'datacontentencoding'", () => {
-      expect(cloudevent.getDataContentEncoding()).to.equal(dataContentEncoding);
+      cloudevent.dataContentEncoding(dataContentEncoding);
+      expect(cloudevent.spec.payload.datacontentencoding)
+        .to.equal(dataContentEncoding);
+      delete cloudevent.spec.payload.datacontentencoding;
     });
 
     it("Should have 'datacontenttype'", () => {
@@ -162,8 +164,51 @@ describe("CloudEvents Spec v0.3", () => {
     });
 
     describe("'datacontentencoding'", () => {
-      it("should throw an erro when 'data' is not a string", () => {
+      it("should throw an error when 'data' is not a string", () => {
+        cloudevent
+          .dataContentEncoding(dataContentEncoding);
+        expect(cloudevent.format.bind(cloudevent))
+          .to
+          .throw("invalid payload");
+        cloudevent.data(data);
+        delete cloudevent.spec.payload.datacontentencoding;
+      });
 
+      it("should throw an error when is a unsupported encoding" , () => {
+        cloudevent
+          .data("Y2xvdWRldmVudHMK")
+          .dataContentEncoding("binary");
+        expect(cloudevent.format.bind(cloudevent))
+          .to
+          .throw("invalid payload");
+        delete cloudevent.spec.payload.datacontentencoding;
+        cloudevent.data(data);
+      });
+
+      it("should accept when 'data' is a string", () => {
+        cloudevent
+          .data("Y2xvdWRldmVudHMK")
+          .dataContentEncoding("base64");
+        expect(cloudevent.format()).to.have.property("datacontentencoding");
+        delete cloudevent.spec.payload.datacontentencoding;
+        cloudevent.data(data);
+      });
+    });
+
+    describe("'subject'", () => {
+      it("should throw an error when is an empty string", () => {
+        cloudevent.subject("");
+        expect(cloudevent.format.bind(cloudevent))
+          .to
+          .throw("invalid payload");
+        cloudevent.subject(type);
+      });
+    });
+
+    describe("'time'", () => {
+      it("must adhere to the format specified in RFC 3339", () => {
+        cloudevent.time(time);
+        expect(cloudevent.format()["time"]).to.equal(time.toISOString());
       });
     });
   });