ExternProtoDeclare

ExternProtoDeclare is a declaration used in the X3D and VRML families of scene-graph languages to indicate that a prototype (a reusable node type) is defined in an external file. It allows authors to reference externally defined prototypes without duplicating their definitions in the current file, facilitating modular design and reuse across scenes and libraries.

In practice, ExternProtoDeclare provides two essential pieces: the name of the prototype and the location of its external definition. The name identifies the external prototype, while a url attribute lists one or more external files and, if necessary, a portion after a hash sign that identifies the specific ProtoDeclare within that file. A nested ProtoInterface may be included to describe the fields that external instances will expose, including their types and access types (initializeOnly, inputOutput, etc.).

Usage typically involves placing an ExternProtoDeclare in a scene to declare the external prototype, followed by a ProtoInstance in the same or other files that creates concrete instances of that external prototype by referring to its name. Example: ExternProtoDeclare { name="AnimatedBox" url=["./AnimatedBox.x3d#AnimatedBox"] ProtoInterface { field { name="size" type="SFVec3f" accessType="inputOutput"} } }. ExternProtoDeclare contrasts with ProtoDeclare, which defines a prototype inline; ExternProtoDeclare only declares the existence of an external prototype and its interface and location.

See also ProtoDeclare, ProtoInterface, ProtoInstance.