docs(legend): correct the key-offset direction semantics

src/gleplot/axes.py

@@ -2382,7 +2382,9 @@ def legend(self, loc: str = "best", **kwargs):
         if "offset" in kwargs:
             # gleplot extension (not a matplotlib kwarg): displace the key
             # from its anchor by (dx, dy) IN CM, GLE's ``key ... offset``.
-            # Positive dy moves DOWN from the anchor, following GLE.
+            # GLE displaces INWARD from the anchored corner: for pos tr,
+            # positive dx moves LEFT and positive dy moves DOWN (verified by
+            # compiled pixel-diff; negative values can leave the canvas).
             offset = kwargs.pop("offset")
             if offset is None:
                 self.legend_offset = None

src/gleplot/writer.py

@@ -1382,8 +1382,12 @@ def add_legend(
             ``nobox``.
         offset : tuple of (float, float), optional
             Displacement of the key from its anchor, in cm, emitted as GLE's
-            ``offset dx dy``. GLE's convention: positive dx moves right,
-            positive dy moves down from the anchor. ``None`` omits the token.
+            ``offset dx dy``. GLE displaces the key INWARD from the anchored
+            corner (verified against GLE 4.3.10 by compiled pixel-diff): for a
+            right-anchored key positive dx moves LEFT, for a top-anchored key
+            positive dy moves DOWN. Negative values push the key outside the
+            graph and can move it off-canvas entirely. ``None`` omits the
+            token.
 
         Notes
         -----