fix: apply curve-pair constraints to sketch preselection

docs/book/src/guide/sketching.md

@@ -60,6 +60,11 @@ midpoint, symmetry, fix, curvature (G2) and polygon. **Sketch Dimension** (D) ad
 aligned, horizontal, vertical, radius, diameter and angle dimensions. Each is a parameter
 (`d1`, `d2`, …), so it can hold an expression.
 
+For Parallel, Perpendicular, Equal, Tangent, Concentric and Collinear, select exactly two
+sketch curves (Shift-click to add the second) and choose the constraint to apply it immediately.
+You can also start the constraint first and then pick its curves. An incomplete or mixed
+selection starts that pick workflow; a rejected constraint keeps the selection for correction.
+
 Under-constrained geometry is blue and fully constrained geometry turns dark, and the status
 shows the remaining degrees of freedom. A constraint or dimension that would over-constrain the
 sketch is refused rather than applied. Drag a point to move it; the solver keeps every