clarify that path.sketch/validate_sketch is looking for string list of three elements

Author: story645

lib/matplotlib/mpl-data/matplotlibrc

@@ -669,14 +669,14 @@
 #path.snap: True  # When True, rectilinear axis-aligned paths will be snapped
                   # to the nearest pixel when certain criteria are met.
                   # When False, paths will never be snapped.
-#path.sketch: None  # May be None, or a 3-tuple of the form:
-                    # (scale, length, randomness).
-                    #     - *scale* is the amplitude of the wiggle
-                    #         perpendicular to the line (in pixels).
-                    #     - *length* is the length of the wiggle along the
-                    #         line (in pixels).
-                    #     - *randomness* is the factor by which the length is
-                    #         randomly scaled.
+#path.sketch: None  # May be None, or a triplet of the form:
+                    #  path.sketch: scale, length, randomness 
+                    # - *scale* is the amplitude of the wiggle
+                    #    perpendicular to the line (in pixels).
+                    # - *length* is the length of the wiggle along the
+                    #    line (in pixels).
+                    # - *randomness* is the factor by which the length is
+                    #    randomly scaled.
 #path.effects:
 
 

lib/matplotlib/rcsetup.py

@@ -562,7 +562,7 @@ def validate_sketch(s):
     try:
         return tuple(_listify_validator(validate_float, n=3)(s))
     except ValueError:
-        raise ValueError("Expected a (scale, length, randomness) triplet")
+        raise ValueError("Expected a 'scale, length, randomness' triplet")
 
 
 def _validate_greaterthan_minushalf(s):