TextUnderlinePositionStyle

This keyword allows the browser to use an algorithm to choose between under and alphabetic. --MDN

In vertical writing-modes, this keyword forces the line to be placed on the left of the characters. In horizontal writing-modes, it is a synonym of under. --MDN

In vertical writing-modes, this keyword forces the line to be placed on the right of the characters. In horizontal writing-modes, it is a synonym of under. --MDN

This keyword forces the line to be set below the alphabetic baseline, at a position where it won't cross any descender. This is useful to prevent chemical or mathematical formulas, which make a large use of subscripts, to be illegible. --MDN

The inherit CSS keyword causes the element for which it is specified to take the computed value of the property from its parent element. --MDN

The initial CSS keyword applies the initial (or default) value of a property to an element. --MDN

The revert CSS keyword reverts the cascaded value of the property from its current value to the value the property would have had if no changes had been made by the current style origin to the current element. --MDN

The unset CSS keyword resets a property to its inherited value if the property naturally inherits from its parent, and to its initial value if not. In other words, it behaves like the inherit keyword in the first case, when the property is an inherited property, and like the initial keyword in the second case, when the property is a non-inherited property. --MDN