[x3d-public] url MFString handling

[Andreas Plesch]

x3dom currently lacks support for back-up urls to use if the first
urls do not work. I am trying to add support and wonder how to deal
with corner cases.

The spirit of the spec. here is pretty clear:
https://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/networking.html#X3DUrlObject

says that a url which cannot be located or if the retrieved data
cannot be interpreted should be skipped. Subsequent urls are then used
as back-ups.

Currently, x3dom checks if an inline x3d url can be parsed as xml and
if so if it has a Scene element.

The first corner case happens if there is a X3D element but it does
not contain a Scene element. This could be interpreted to mean an
empty X3D document with an empty Scene, or that it perhaps should be
skipped as not interpretable. I would probably favor skipping as this
would normally happen by mistake.

The second corner case is a Scene element without content. Should such
X3D be considered interpretable ?  I think x3dom is currently set up
to parse it without error resulting in an empty Scene, probably with
default NavigationInfo and Viewpoint. So this could be considered
interpretable and not be skipped.

https://www.web3d.org/x3d/content/examples/X3dSceneAuthoringHints.html#urls

says a result needs to be "legal". But legal is by definition what is
provided in the spec., eg. comes down to being interpretable.

The tooltip at https://www.web3d.org/x3d/content/X3dTooltips.html#Inline.url

does not seem to further clarify.

Any feedback appreciated,

Andreas

--
Andreas Plesch
Waltham, MA 02453