Inline-block displays

Dear Sirs,

    In checking my style sheet with your validator, I get this message:

        "Invalid number : display inline-block is not a display value : inline-block".

    However, per Eric A. Meyer's Cascading Style Sheets (p. 448), this is definitely a display value ... and a very useful one, needless to say. 

    My documents are done in XHTML 1.0 Transitional, and validate correctly with the W3C Validator designed for that purpose. 

    Your own validator unfortunately does not give or refer to more detailed explanations.

    Could you please clarify this situation?

            Sincerely,

                       Paul Nelson