Merge pull request #8268 from janetournois/Mesh_3-fix_concept-jtournois

Mesh_3 - fix concept `MeshFacetCriteria_3`

Mesh_3/doc/Mesh_3/Concepts/MeshFacetCriteria_3.h

@@ -62,6 +62,11 @@ a natural model of this concept.
 */
 typedef unspecified_type Is_facet_bad;
 
+/*!
+* Numerical type.
+*/
+typedef unspecified_type FT;
+
 /// @}
 
 /// \name Operations
@@ -73,6 +78,12 @@ The type `Tr` must be identical to the triangulation type used by the mesh gener
 */
 Is_facet_bad operator()(const Tr& tr, Facet f);
 
+/**
+* @returns the squared value of minimal radius bound if set,
+* and `std::nullopt` otherwise
+*/
+std::optional<FT> squared_min_radius_bound() const;
+
 /// @}
 
 }; /* end MeshFacetCriteria_3 */

Mesh_3/include/CGAL/Mesh_facet_criteria_3.h

@@ -179,6 +179,10 @@ class Mesh_facet_criteria_3
     return topology_;
   }
 
+  /**
+  * @returns the squared value of minimal radius bound if it was set,
+  * and `std::nullopt` otherwise
+  */
   std::optional<FT> squared_min_radius_bound() const {
     if(squared_min_radius_bound_)
       return *squared_min_radius_bound_;