x-use-underline-position-properties

x-use-underline-position-properties is a variable defined in `C source code'.
Its value is

t

Documentation:
Non-nil means make use of UNDERLINE_POSITION font properties.
A value of nil means ignore them. If you encounter fonts with bogus
UNDERLINE_POSITION font properties, for example 7x13 on XFree prior
to 4.1, set this to nil. You can also use `underline-minimum-offset'
to override the font's UNDERLINE_POSITION for small font display
sizes.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.1 of Emacs.