All of the following elements indicate an Income Withholding Order is "regular on its face"...

Comprehensive and Detailed in-Depth Explanation:

An Income Withholding Order (IWO) is considered "regular on its face" if it appears to be an authentic and complete legal document. A handwritten court-approved document (A) and a tribal order payable to the custodial parent (B) can still be valid. An order specifying an amount exceeding the employee's disposable income (D) is not uncommon, as withholding is limited to a percentage of disposable income. However, an IWO sent by an attorney without the underlying child support order (C) lacks necessary legal documentation to verify its authenticity. Therefore, the correct answer is C. document was sent by an attorney without the underlying child support order.