Hi,
I am experimenting with some of the Ruby on Rails JavaScript generators
and see something I haven't before. Maybe it is worthwhile?
In the page below the script is enclosed in
//<![CDATA[
//]]>
Is this trick grounded in any real information about HTML vs XHTML? I
think what they are trying to achieve is a way to generate a script
block that can be used in either HTML or XHTML. Have they managed that
goal? It looks fine for HTML but will the double slashes be ok in
XHTML?
Thanks,
Peter
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Fork JavaScript</title>
</head>
<body>
<script type="text/javascript">
//<![CDATA[
new Form.Element.Ob server('search' , 0.5, function(elemen t, value) {new
Ajax.Updater('r esults', '/cont/search', {asynchronous:t rue,
evalScripts:tru e, parameters:valu e})})
//]]>
</script>
</div>
</body>
</html>
12  4011 
Peter Michaux wrote:
//<![CDATA[
//]]>
Is this trick grounded in any real information about HTML vs XHTML? I
think what they are trying to achieve is a way to generate a script
block that can be used in either HTML or XHTML. Have they managed that
goal? It looks fine for HTML but will the double slashes be ok in
XHTML?
Yes, this is not anything unique to Rails. This is SGML for "ignore
whatever comes between these marks". The leading slashes are OK
because they have no significance in SGML syntax. This is supposed to
prevent the parser from misreading any characters that would otherwise
be read as markup, such as angle brackets (and <) which have a
different meaning in javascript : http://www.w3.org/TR/REC-xml/#sec-cdata-sect
David
Peter Michaux wrote:
Hi,
I am experimenting with some of the Ruby on Rails JavaScript
generators and see something I haven't before. Maybe it is worthwhile?
In the page below the script is enclosed in
//<![CDATA[
//]]>
Is this trick grounded in any real information about HTML vs XHTML?
Not really, It is a cargo cult/mystical incantation thing. In HTML the
contents of SCRIPT elements are CDATA anyway and the two lines posted
are just end of line comments. In XHTML the contents of SCRIPT elements
are PCDATA, but there is no need to attempt to comment out the CDATA
block mark-up. And as it is largely impractical to write non-trivial
scripts that will function with both HTML DOMs and XHTML DOMs there is
no need for a construct to 'normalise' SCRIPT element contents to CDATA
for use with both types of DOM.
I think what they are trying to achieve is a way to
generate a script block that can be used in either
HTML or XHTML.
They may think that they are trying to do that, but probably without any
understanding of the differences between an XHTML DOM and an HTML DOM,
and so no appreciation of the worthlessness of the exercise.
Have they managed that goal?
Yes, but the scripts being inserted into that construct are extremely
unlikely to work if the mark-up that contains them is ever interpreted
as XHTML and an XHTML DOM exposed to the script. Which renders the
effort moot.
It looks fine for HTML but will the double slashes be
ok in XHTML?
They will be fine, it is the scripts they contain that will likely go
belly-up if the documents are ever interpreted as XHTML by a web
browser.
Richard.
David Golightly wrote:
Peter Michaux wrote:
>//<![CDATA[
//]]>
Is this trick grounded in any real information about HTML vs
XHTML? I think what they are trying to achieve is a way to
generate a script block that can be used in either HTML or
XHTML. Have they managed that goal? It looks fine for HTML
but will the double slashes be ok in XHTML?
Yes, this is not anything unique to Rails.
That is certainly true. Rails is not the only system that includes
spurious constructs in mark-up for no particularly good reason.
This is SGML for "ignore
whatever comes between these marks".
Nonsense. The <![CDATA[ ... ]]mark up in XML is adopted directly form
SGML and has exactly the same meaning in both. In the context of the
contents of an HTML SCRIPT element, which is already CDATA, the
construct has no significance as such contents are not parsed for
mark-up, beyond identifying where they end.
The leading slashes are OK
because they have no significance in SGML syntax.
No, they are OK because the contents of an HTML SCRIPT element are CDATA
and so not mark-up at all, and the contents of an XHTML script element
are PCDAT and so the slashes outside the <![CDATA[ and ]]delimiters
will be parsed and the (unchanged) results used as part of the script
source code, with the unparsed contents of the CDATA block inserted in
place of the CDATA delimiters.
This is supposed to prevent the parser from misreading any
characters that would otherwise be read as markup, such as
angle brackets (and <) which have a different meaning in
javascript:
And is worthless in an HTML document where no such misinterpretati on is
possible, while in an XHTML document there is no need for the end of
line comment syntax.
Richard.
Richard Cornford wrote:
Peter Michaux wrote:
Hi,
I am experimenting with some of the Ruby on Rails JavaScript
generators and see something I haven't before. Maybe it is worthwhile?
In the page below the script is enclosed in
//<![CDATA[
//]]>
Is this trick grounded in any real information about HTML vs XHTML?
Not really, It is a cargo cult/mystical incantation thing. In HTML the
contents of SCRIPT elements are CDATA anyway and the two lines posted
are just end of line comments. In XHTML the contents of SCRIPT elements
are PCDATA, but there is no need to attempt to comment out the CDATA
block mark-up. And as it is largely impractical to write non-trivial
scripts that will function with both HTML DOMs and XHTML DOMs there is
no need for a construct to 'normalise' SCRIPT element contents to CDATA
for use with both types of DOM.
I think what they are trying to achieve is a way to
generate a script block that can be used in either
HTML or XHTML.
They may think that they are trying to do that, but probably without any
understanding of the differences between an XHTML DOM and an HTML DOM,
and so no appreciation of the worthlessness of the exercise.
I haven't read anything about how a script would have to be written
differently depending if it is in an HTML document or an XHTML document
(being correctly interpreted as XHTML).
Do you have a tiny example or pointer to some information about this?
Thanks,
Peter
Richard Cornford wrote:
David Golightly wrote:
This is SGML for "ignore
whatever comes between these marks".
Nonsense. The <![CDATA[ ... ]]mark up in XML is adopted directly form
SGML and has exactly the same meaning in both. In the context of the
contents of an HTML SCRIPT element, which is already CDATA, the
construct has no significance as such contents are not parsed for
mark-up, beyond identifying where they end.
Richard - Read once more what I wrote, then what you wrote, then cool
down for once, then tell me how they disagree with each other.
Richard Cornford wrote:
David Golightly wrote:
Yes, this is not anything unique to Rails.
The leading slashes are OK
because they have no significance in SGML syntax.
No, they are OK because the contents of an HTML SCRIPT element are CDATA
and so not mark-up at all, and the contents of an XHTML script element
are PCDAT and so the slashes outside the <![CDATA[ and ]]delimiters
will be parsed and the (unchanged) results used as part of the script
source code, with the unparsed contents of the CDATA block inserted in
place of the CDATA delimiters.
That's exactly what I said. Thanks for reiterating.
>
This is supposed to prevent the parser from misreading any
characters that would otherwise be read as markup, such as
angle brackets (and <) which have a different meaning in
javascript:
And is worthless in an HTML document where no such misinterpretati on is
possible, while in an XHTML document there is no need for the end of
line comment syntax.
Sorry Richard, you're off base on this one. Case in point: closing
tags in script strings. Consider the following code:
<script type="text/javascript">
//<!--
var myScriptTag = '<script type="text/javascript
src="foo.js"></script>';
//-->
</script>
As we all know, older HTML parses will barf at the literal closing
</scripttag in the string. That's why you see strings broken up
like:
'<'+'/script' etc.
so browsers don't mistake this for an HTML element and parse it
mistakenly. (See Flanagan, javascript : TDG, 5th Edition, page 247).
With a CDATA section explicitly defined, this problem doesn't occur and
coders don't have to worry about this mistake. This alone, and the
fact that the CDATA tag doesn't add any other drawbacks over the
conventional <!-- --comment, make this a preferred approach for
commenting out script sections.
Peter Michaux wrote:
Hi,
I am experimenting with some of the Ruby on Rails JavaScript generators
and see something I haven't before. Maybe it is worthwhile?
In the page below the script is enclosed in
//<![CDATA[
//]]>
Is this trick grounded in any real information about HTML vs XHTML?
There is a possibility that if a parser encounters "</" or "</script>"
within a script it may be interpreted as an end of script element tag,
and anything after may be thought of as markup.
The simple solution is to use external scripts. If the script is
included in the page, wherever "</" might be encountered either:
1. separate the "<" and "/" with a space: "< /"
2. use a backslash to quote it: "<\/"
as appropriate. I can't think of a case to use the former as I don't
think it's legal ECMAScript syntax (but it might occur in some other
script language), the latter can be used where HTML is included in the
script, say as innerHTML or with document.write.
ISTM much better to deal with those cases as they occur, rather than
with the blanket inclusion of comment delimiters which are otherwise
pointless.
--
Rob
Peter Michaux wrote:
Richard Cornford wrote:
>Peter Michaux wrote:
<snip>
>>In the page below the script is enclosed in
//<![CDATA[
//]]>
<snip>
>>I think what they are trying to achieve is a way to
generate a script block that can be used in either
HTML or XHTML.
They may think that they are trying to do that, but probably
without any understanding of the differences between an XHTML
DOM and an HTML DOM, and so no appreciation of the
worthlessnes s of the exercise.
I haven't read anything about how a script would have to be
written differently depending if it is in an HTML document
or an XHTML document (being correctly interpreted as XHTML).
Why would you expect to? There is no commercial application for
client-side scripting of XHTML for as long as IE is not capable of
interpreting XHTML and creating an XHTML DOM to be scripted.
Do you have a tiny example or pointer to some information
about this?
Examples are posted to the group, maybe not frequently but regularly
enough to make it obvious that most who wander into XHTML DOM scripting
are not expecting what they find. An archive search (probably restricted
to the last 5 years or so) with keywords corresponding to the namespace
qualified DOM menthols (such as - createElementNS - or -
setAttributeNS -) should turn a number of real life examples (as
namespace qualified methods need to be used with XHTML DOMs).
Richard.
David Golightly wrote:
Richard Cornford wrote:
>David Golightly wrote:
>>This is SGML for "ignore
whatever comes between these marks".
Nonsense. The <![CDATA[ ... ]]mark up in XML is adopted
directly form SGML and has exactly the same meaning in both.
In the context of the contents of an HTML SCRIPT element,
which is already CDATA, the construct has no significance as
such contents are not parsed for mark-up, beyond identifying
where they end.
Richard - Read once more what I wrote,
I did read what you wrote, it was, "ignore whatever comes between theses
marks", and that is very much not true. SGML includes the marked section
keyword IGNORE so that if it does need to "ignore whatever comes between
theses marks" that facility exists. CDATA is not ignored it is just not
parsed (beyond scanning for its closing delimiter).
then what you wrote, then cool
down for once, then tell me how they disagree with
each other.
The CDATA marked section is not ignored in XHTML as its contents must
contribute to the source characters that will be interpreted as script,
and in HTML there is no CDATA marked section within the SCRIPT element
as the SCRIPT element's contents are already CDATA and so the
<![CDATA[ and ]]delimiters are just sequences of text characters. That
is; in XHTML they are not ignored and in HTML they never existed as
mark-up and so could not mark their contents as to be ignored.
Richard. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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