`defaultLinkAnchor` - a link anchor function that is used by links if no `linkAnchor` property is defined for a link end. It can either be an object (with a `name` and optional `args`) or a function. JointJS provides a collection of built-in link anchor functions in the `joint.linkAnchors` namespace; alternatively, a custom function may be provided. See the link geometry linkAnchor documentation for more information.