[x3d-public] Backslashes in X3D XML in SFString

Michalis Kamburelis michalis.kambi at gmail.com
Wed May 10 17:33:46 PDT 2017


Short version: I tested how do the existing X3D browsers treat
backslashes in SFString and MFString in X3D XML encoding. The results
are conclusive:

- backslashes are NOT used for escaping inside SFString
- backslashes are used for escaping inside MFString

This confirms my suggestions during today's Web3d teleconference.
SFString and MFString in XML encoding do *not* treat the backslash the
same way (at least in current implementations). So if we want to fix
the specification such that it matches the current implementations ->
we should preserve this.

My suggested corrections (in the attached "corrections.txt", attaching
it here again) account for this: they explicitly say that backslashes
are only for MFString.

The tests and screenshots are on

Longer version:

During the talk today at Web3d Teleconference, we discussed the use of
backslashes inside X3D XML MFString and SFString.


The X3D XML specification (
) unfortunately doesn't say much about backslashes. It only shows an

  <Text string='"He said, \"Immel did it!\""' />

To confuse matters more, the above example in X3D XML spec is titled
"[...] the following SFString field string:" but it's obviosuly an
MFString example (because Text.string is in fact MFString, and because
there are additional double-quotes without backslashes inside).

OK, regardless of what does the specification say, what do the
implementations do?

1. Everyone agrees that backslashes are necessary in X3D XML for
MFString. Otherwise, when reading MFString value, you don't know
whether some double-quote should be visible, or whether it's a
delimiter that ends this part of MFString.

  Testing on:
  - FreeWRL
  - Instant Reality
  - BS Contact
  - Octaga Player
  - View3dscene (my own)

  All these browsers honor the backslashes as expected... *except* Octaga.

  But Octaga displays a weird characters here (see
). I think we can safely say that this is just some bug in Octaga, and
ignore Octaga for this test.

2. The interesting question is whether backslashes are used (as an
escape character) in X3D XML for SFString.

  - On one hand, it would seem consistent, to have the same rule about
backslashes for SFString and MFString.
  - On the other hand, they are not necessary for SFString (no need to
escape double-quotes inside SFString in X3D XML). So the X3D browser
can just "take" the value of the XML attribute as an SFString value.

  I proposed to check what the existing specifications are doing.

  The testcase isn't trivial. Existing X3D nodes use mostly MFString
for a "free text" (URLs, or for Text.string). The SFString is mostly
used only for "enumerated" fields where a limited set of values is
valid. So I implemented a testcase using a Script node, that takes two
SFString values, and sends them into the Text.string (which is of
MFString type).

  The results of this testcase on

  - FreeWRL
  - Instant Reality
  - BS Contact

  are consistent, and show that the backslashes were NOT interpreted
as escape characters inside SFString.

  The result of my view3dscene on this testcase is not useful (as I
don't support JavaScript now, only CastleScript and Object Pascal).
But I know that my implementation is consistent with the above:
backslashes in SFString (in X3D XML) are NOT for escaping.

  The result of Octaga on this testcase is not useful, because it only
shows more weirdness.

Please feel free to test my testcase on other browsers.

This was all tested on the latest versions of mentioned browsers,
downloaded today, on 64-bit Windows.

Best regards,
-------------- next part --------------
The proposed change to the specification (all to the section
) would be to change this part:

  The MFString specifies zero or more SFStrings enclosed in single
quotes (e.g., '"string1" "string2"').

  NOTE  The construct


is not a valid instance of an MFString. Such an MFString would be
properly specified as


into this:

  The MFString specifies zero or more SFStrings, with each single
string enclosed in double quotes (e.g., "string1" "string2"). Note
that inside an XML attribute, you have to express a double quote using
the " character entity, unless you enclose a whole XML attribute
in single quotes.

  NOTE  The construct


is not a valid instance of an MFString. Such an MFString would be
properly specified as






For additional clarity, I would also add more prose and examples to
explain when backslashes are needed. So I would change

EXAMPLE 2  Two instances of the double quote are contained in the
following SFString field string:

<Text string='"He said, \"Immel did it!\""' />

with this:

If a string is part of an MFString, and you want this string to
contain a double-quote (for example, to actually show a double-quote
using the Text node field "string") then you have to place a backslash
before this double-quote. This rule applies regardless if you express
double-quote as " or as " . This is necessary, to avoid treating
the double-quote as a delimiter of strings on a MFString list.

Consequently, if you want a string inside MFString to contain a
backslash (for example, to actually show a backslash using the Text
node field "string") then you have to write two backslashes. This is
necessary, to avoid accidentally changing the meaning of a following
double-quote character.

EXAMPLE 2  All the following forms are correct and equivalent:

<Text string='"He said, \"Immel did it!\""' />

<Text string='"He said, \"Immel did it!\""' />

<Text string='"He said, \"Immel did it!\""' />

<Text string=""He said, \"Immel did it!\""" />

  SFString specifies a single string encoded as a sequence of UTF-8
octets enclosed in double quotes (e.g., "string").

could be changed to

  SFString specifies a single string encoded as a sequence of UTF-8
octets. It is simply the value of an XML attribute. As such, following
XML rules, it can be surrounded either in single-quotes (apostrophes)
or double quotes.

The following examples of an SFString are all valid:

"string "with some quotes inside""
'string "with some quotes inside"'
'string "with some quotes inside"'

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