Try the below steps to accomplish this. Some modification might be needed, but this should work with most HTML 5 objects with the ''required'' tag.

Troubleshooting example can be found on [http://www.w3schools.com/html/tryit.asp?filename=tryhtml5_input_required][1]

1. Open the object repository and highlight Test Objects in the left pane.
2. Click the Define New Test Object icon.
3. Set the following properties:
Environment: Web
Class: Page
Name: Whatever you want. For this example, we'll call it Validator
4. Click Add.
5. Click the Validator object in the object tree.
6. Change the Ordinal Identifier to Type:Index, Value:0
7. With the Validator page still highlighted, click the Define New Test Object icon again.
8. Set the following properties:
Environment: Web
Class: WebElement
Name: Whatever you want. For this example, we'll call it Validation
html tag: DIV
html id: contentContainer
Delete any other properties that are present
9. Click Add.
10. In your test, do whatever causes the validation message to appear.
11. Use the following code to grab the text of the validation message:

strMessage = Page(''Validator'').WebElement(''Validation'').GetROProperty(''innertext'')

Now you can validate that strMessage contains the text you expect.

[1]: http://www.w3schools.com/html/tryit.asp?filename=tryhtml5_input_required