diff --git a/master/painting.html b/master/painting.html
index 11424472..a4fb3489 100644
--- a/master/painting.html
+++ b/master/painting.html
@@ -762,7 +762,8 @@ <h3 id="StrokeWidth">Stroke width: the <span class="property">'stroke-width'</sp
 
 <p>This property specifies the width of the stroke on the current object.
 A zero value causes no stroke to be painted. A negative value
-is <a>invalid</a>. A <a>&lt;number&gt;</a> value represents a value in <a>user units</a>.</p>
+is <a>invalid</a>. A <a>&lt;number&gt;</a> value represents a value in <a>user units</a>.
+By default, the stroke is centered on the border, and therefore paints beyond the shape by half of the stroke-width.</p>
 
 <h3 id="LineCaps">Drawing caps at the ends of strokes: the <span class="property">'stroke-linecap'</span>
 property</h3>
@@ -1446,7 +1447,7 @@ <h3 id="StrokeShape">Computing the shape of the stroke</h3>
               <li>Let <var>dash</var> be the shape that includes, for all distances
               between <var>start</var> and <var>end</var> along the subpath, all
               points that lie on the line perpendicular to the subpath at that
-              distance and which are within distance <a>'stroke-width'</a> of
+              distance and which are within distance <a>'stroke-width'</a> / 2 of
               the point on the subpath at that position.</li>
 
               <li>Set <var>dash</var> to be the union of <var>dash</var> and the