diff --git a/index.html b/index.html
index d1c590c..747fb01 100755
--- a/index.html
+++ b/index.html
@@ -398,7 +398,11 @@ <h3 id="placement-of-mono-ruby">Placement of mono-ruby</h3>
  (see [[[#line-start-mono]]]),
  while if the annotation falls at the end of the line,
  then the end of the ruby annotation is aligned with the line’s end edge
- (see [[[#line-end-mono]]]).</p>
+ (see [[[#line-end-mono]]]).
+ Although spacing could be inserted between ruby base and the line edge following this rule, 
+ results of placement are allowed if ruby annotation is aligned with the line edge. 
+ This rule was used in [[?JISX4051]] and also in real cases.
+</p>
  
 <figure id="line-start-mono"> <img src="img/fig10.svg" alt="" style="min-width: 11em;" />
 <figcaption>Example of mono-ruby at the line start.</figcaption>