Visual indicator requirement for using H28 - Providing definitions for abbreviations by using the abbr element

Question on technique H28 - Providing definitions for abbreviations by using the abbr element (https://www.w3.org/WAI/WCAG22/Techniques/html/H28)

When using this technique and the abbr tag to define abbreviations, is there a requirement that a visual indicator exists such as the dashed underline to show there is a hover over definition for the abbr? Or an the visual indicator be disabled?

Thank you