Minimal changes to avoid fatal errors only

Author: foolip

index.bs

@@ -8433,8 +8433,8 @@ Return <a>success</a> with data <var>action</var>.
   <var>target x</var> and <var>y</var> equal <var>target y</var>.
 
   <p>Otherwise let <var>x</var> equal an approximation
-   to <var>duration ratio</var> &times; (<var>target x</var>
-   - <var>start x</var>) + <var>start x</var>, and <var>y</var> equal
+   to <var>duration ratio</var> &times; (<var>target x</var> -
+   <var>start x</var>) + <var>start x</var>, and <var>y</var> equal
    an approximation to <var>duration ratio</var> &times;
    (<var>target y</var> - <var>start y</var>) + <var>start y</var>.