1 files changed, 2 insertions, 0 deletions

diff --git a/src/xterm.c b/src/xterm.c
index 2371058cd45..0d25c7f1a26 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -13250,6 +13250,8 @@ small font display sizes.  */);
   DEFVAR_BOOL ("x-underline-at-descent-line",
                x_underline_at_descent_line,
      doc: /* Non-nil means to draw the underline at the same place as the descent line.
+(If `line-spacing' is in effect, that moves the underline lower by
+that many pixels.)
 A value of nil means to draw the underline according to the value of the
 variable `x-use-underline-position-properties', which is usually at the
 baseline level.  The default value is nil.  */);