Is there a need to add an underline button to rich text?

[t-hamano]

I noticed that of all the format types in the core, only the underline is not showing up in the toolbar or dropdown.
Below are the results of the survey:

Format Type	Shown in the toolbar?	Mentioned in shortcut modal?	Have a shortcut? (On Windows)
core/bold	✅ (toolbar)	✅	✅ ( Ctrl + B )
core/code	✅ (toolbar)	✅	✅ ( Shift + Alt + X )
core/image	✅ (dropdown)	-	-
core/italic	✅ (toolbar)	✅	✅ ( Ctrl + I )
core/link	✅ (toolbar)	✅	✅ ([[)
core/striktthrough	✅	✅	✅ ( Shift + Alt + D )
core/underline	⚠️	✅	✅
core/text-color	✅	-	-
core/subscript	✅	-	-
core/superscript	✅	-	-
core/keyboard	✅	-	-

Looking at this table alone, it seems odd that only the underline doesn't have a button, but this feature is not a deprecated "Underline" element, but simply wraps in a span tag with an underline style.

#13117 is the PR with an additional underline shortcut by Cmd + U.
I also consulted the relevant issue, and it is my understanding that the underline style does not explicitly provide a button because it could be confused with the inline style.

Personally, I sometimes want to give an underline that is not a link, but is there any possibility of a button being added in the future?

[jasmussen]

I do not have the full history, but it is my understanding that the underline button is intentionally not surfaced because underlined text carries with it a risk of being confused with a hyperlink. This is especially important for low-vision or color-blind users, for whom usually colored hyperlinks may not be sufficiently differentiated from underlined text. Having the shortcut available, but the button not surfaced, seems like an acceptable balance to me.

[t-hamano]

Thank you for the detailed explanation.
That certainly makes sense.

[scruffian]

The problem is that in some themes, underlines are explicitly removed from links for example: https://github.com/Automattic/themes/blob/ca887cd3f72c1b755c0b5b6d2fe2c85d7597411c/pendant/theme.json#L378

In this case if I want an underlined link outside the Post Content the only way to do it is using a keyboard shortcut.