Sheet metal: an Edge Flange can choose its own corner relief (#1481)

An Edge Flange feature can set the shape and size of the relief at the corners its flanges make, in place of the sheet metal rule's. Design format 24.

Co-authored-by: NOWN-DEV <[email protected]>
Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

docs/book/src/guide/files.md

@@ -86,7 +86,7 @@ is available. Missing or incompatible pictures use the usual thumbnail generatio
 The default `cache: false` omits the portable thumbnail too.
 The repository's `docs/design-container.md` describes limits and encoding details.
 
-Current designs use format 21, including design properties, named render setups, opaque PBR looks, thin extrudes, sheet metal perforation fields, associative editable sketch patterns, editable associative offset-distance dimensions, the style of sketch text (bold, italic, alignment, spacing and the curve it follows), face anchors on a piece of a face by its own name, sheet metal rims and bend ends, bend edges for Convert to Sheet Metal, the tear corner relief of sheet metal rules, the names of projected edges, physical materials defined in the design, the font of sketch text, the expressions behind a sketch text's height, place and angle, sheet metal corner relief shapes, sketch face anchors on cylinder caps, sketch axis
+Current designs use format 24, including the corner relief of an edge flange, the gear, rack and pinion and screw couplings of motion links, design properties, named render setups, opaque PBR looks, thin extrudes, sheet metal perforation fields, associative editable sketch patterns, editable associative offset-distance dimensions, the style of sketch text (bold, italic, alignment, spacing and the curve it follows), face anchors on a piece of a face by its own name, sheet metal rims and bend ends, bend edges for Convert to Sheet Metal, the tear corner relief of sheet metal rules, the names of projected edges, physical materials defined in the design, the font of sketch text, the expressions behind a sketch text's height, place and angle, sheet metal corner relief shapes, sketch face anchors on cylinder caps, sketch axis
 links, persistent
 names from exact face history, exact planar shell-face anchors, persistent analytic offset boundary roles and
 association profile references, durable sketch face anchors, periodic fit splines and versioned

docs/book/src/guide/sheet-metal.md

@@ -64,6 +64,22 @@ warning saying where.
  "bend_radius":"1 mm","corner_relief_shape":"round","corner_relief":"8 mm","active":true}}
 ```
 
+The rule's shape and size are the default. An edge flange feature can choose its own for the
+corners its flanges make: `corner_relief_shape` (`notch`, `round`, `rectangular` or `tear`) and
+`corner_relief` (the size across, a length or an expression) in `sheet.flange`, or Corner Relief
+Shape and Corner Relief in the Flange dialog. In the dialog, Rule as the shape and an empty size
+take the rule's; either one left out follows the rule while the other is the feature's. Corners are
+relieved only between the flanges of one feature, so a feature's choice never meets another's at a
+corner, and two edge flange features of one part can have different reliefs under one rule. A
+base or contour flange takes its corners from the rule only and refuses both parameters. The
+flange gap and the rule's other values stay with the rule for every flange. The feature's choice is
+saved with the design (file format 23).
+
+```json
+{"command":"sheet.flange","params":{"edges":[[60,0,2],[120,45,2],[60,90,2],[0,45,2]],
+ "height":20,"corner_relief_shape":"round","corner_relief":"6 mm"}}
+```
+
 Where the edge flanges of one feature meet at a corner of the base, their panels are closed
 toward each other at any bend angle: each end is cut square to the sheet, on a line in the flat
 chosen so that the edges nearest each other (on the inner faces) run parallel, the rule's