deploy.

App/wwwroot/HiAPI-docsite/technique/nc-dialects/controller-iso.html

@@ -246,7 +246,8 @@ its own for the rest — see <a href="#siemens-sinumerik">Siemens SINUMERIK</a>.
 </table>
 <p>Radius compensation is resolved against the blocks that actually travel in the compensation plane. A
 block whose own words command no movement in that plane — a bare <code>G41</code> / <code>G42</code>, a comment, an empty
-line, a Z-only plunge — takes no offset of its own and no part in a corner:</p>
+line, a plunge along the plane normal (Z under G17) — takes no offset of its own and no part in a
+corner:</p>
 <ul>
 <li><strong>Start-up waits for motion.</strong> A <code>G41</code> or <code>G42</code> block that does not move in the plane does not
 start the offset; the first block that travels in the plane is the start-up block and takes the
@@ -254,8 +255,15 @@ perpendicular (type A) offset. The blocks between them carry the previous block'
 so nothing moves on their account.</li>
 <li><strong>Corners are resolved between travelling blocks.</strong> Wordless blocks sitting between two moves are
 passed over, and the corner is the intersection of the two real segments. Running axes are the
-in-plane part of each displacement, so a ramping move keeps its full offset and a Z-only plunge
-stays on the offset line.</li>
+in-plane part of each displacement, so a ramping move keeps its full offset and a plunge along
+the plane normal stays on the offset line.</li>
+<li><strong>The plane cannot change inside a region.</strong> <code>G17</code> / <code>G18</code> / <code>G19</code> selects the
+compensation plane, and it may only be selected while compensation is cancelled. A plane
+code that resolves to a different plane while <code>G41</code> / <code>G42</code> is active — including one
+sharing its block with the <code>G40</code> that cancels the region — is reported as
+<code>RadiusComp--PlaneChangeInRegion</code>, because the corner spanning the change would be built
+from one running axis per plane. A control alarms there (Fanuc PS0037 CAN NOT CHANGE
+PLANE IN CRC). Re-selecting the plane already in force is not a change and is accepted.</li>
 <li><strong>A bare <code>G40</code> closes the region.</strong> The last compensated block ends on its own perpendicular
 offset rather than turning toward the first uncompensated move after the cancel. A <code>G40</code> that
 carries motion is the last corner's partner instead, and the compensated path meets the cancel