The text-underline-position property sets the position of an underline with respect to the text, and defines its zero position for further adjustment by text-underline-offset.
object.style.textUnderlinePosition = "value";
<'text-underline-position'> = auto | [ from-font | under ] || [ left | right ]
Automatically specified by the user agent.
If the first available font has metrics indicating a preferred underline offset, use that offset, otherwise behaves as auto.
The underline is positioned under the element's text content.
In vertical typographic modes, the underline is aligned as for under, except it is always aligned to the left edge of the text.
In vertical typographic modes, the underline is aligned as for under, except it is always aligned to the right edge of the text.
World Wide Web Consortium (W3C)