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Re: [dom3core] getAttribute

From: Ray Whitmer <ray@personallegal.net>
Date: Wed, 7 Dec 2005 14:58:43 -0700
Message-Id: <EC18655B-0EEE-4FA3-B681-9666A2071285@personallegal.net>
Cc: Brendan Eich <brendan@meer.net>, www-dom@w3.org
To: Maciej Stachowiak <mjs@apple.com>

On Dec 7, 2005, at 1:34 PM, Maciej Stachowiak wrote:

>> Mode 3 is for compliance testing with standards that also work in IE.
>> So we wish to discourage use of getAttribute to check whether the  
>> attribute exists (fail if they do it).
>> Therefore, calling getAttribute on a non-existant attribute in  
>> mode 3 would ideally throw an exception, so that any script that  
>> called getAttribute without knowing whether an attribute existed  
>> first would get an exception in this mode, because due to the  
>> ambiguity / tension between the specification and the status quo,  
>> there is no predicting what happens.
> A mode that did this would not be compliant with the standard and  
> would fail the test suite. So really this is inventing a new kind  
> of nonstandard behavior. This mode would also reject some obvious  
> idioms that work with both the written spec and the de facto standard:
> if (!e.getAttribute("foo")) {
>    // code to run if e is either empty or null
> }

I think it was clear from the initial description that the purpose of  
mode 2 was to pass the de jure test suite as an implementation, and  
neither mode 1 nor mode 3 would pass the de jure test suite, just as  
neither 2 or 3 pass the de facto tests.  That is what subsetting the  
functionality means.  A subset function set does not pass the  
superset of tests.  If all modes could pass all tests, there would be  
little need for modes.  Again, the purpose of mode 3 is for web  
authors to test against, to produce code that will run under either  
mode 1 or mode 2 without problems.  It is not the purpose to have  
other end users run under it, although if they have problems with  
content of a web site, they can recommend it as a test platform to  
the one responsible for it, which helps verify flexibility of web  
content beyond a single platform.

> As well as breaking both compliant code and de facto standard code.

This is the design, purpose, and reason for its existence.  To break  
all code that is not simultaneously compliant with both the de jure  
standard and the de facto standard.  Anywhere there is special code  
that does not meet the standard or the de facto standard, it is  
disabled in mode 3.  The return from getAttribute with a non- 
specified attribute is such behavior.  Therefore, when the browser  
reaches that place, it gives up because that is not implemented.   
Therefore, code which is written that cannot satisfy both, fails.  It  
is created as a better test, which allows web authors to more-easily  
write code compliant with both de jure and de facto standards.  It is  
fairly trivial to write around the definitional problems if they are  
flagged for you.

> Furthermore, since the error only occurs at runtime, you might  
> never go through the code path where it comes up and so could never  
> tell your code was right.

That is true of all testing of web apps in a browser built on  
Javascript.  Or do you use something better? But at least you don't  
wind up thinking your web app works in cases where you did test where  
it is relying on behavior that is not specified the same way for the  
de jure and de facto standards.  So it is not as treacherous for  
testing as a normal web browser that happily satisfies requests that  
are not in line with any particular standard that in many cases are  
not expected to work the same between browsers.  So when you write  
behavior into the browser that has issues with the de jure or de  
facto standard compatibility, you just add a mode check and prevent  
it from occurring if the browser is being used to verify the  
functionality of a web app.  Fairly strait-forward, fairly useful.

> I don't think adding a new  mode that is both noncompliant *and*  
> incompatible with existing content would be very helpful.

The content cases that successfully run in the mode 3 without hitting  
special exceptions are both compliant and compatible (the special  
exceptions could be made non-catchable just to make sure).  In order  
to do that, it cannot be a compatible or compliant end-user browsing  
mode DOM implementation, because it must rule out things that are not  
compliant and compatible in both mode 1 and mode 2, even if they are  
defined to work in 1 or 2, or 1 and 2 differently.

By way of comparison, a C lint verifier tool also fails to be  
compatible with many forms of C (without generating errors), because  
that is it's express purpose, to find problems that the lax standard  
let through and thereby improve the code of an author.  But the C  
code that passes the verifier is all standard, higher quality, and  
more-portable (assuming that is the sort of thing the lint tool is  
looking for).  Mode 3 is such a tool.  Mode 3 is restricted to  
runtime checks, just as lint is restricted to compile time checks  
(there are other runtime tools).  In each case, it is a stricter mode  
of the tools that helps weed out problematic cases.  End users do not  
use lint to execute their code any more than mode 3 is used by end  
users.  Slowly, to really reach the developers, lint-like checking is  
integrated into C compilers as special checking modes and the de jure  
standard bar is even raised hand in hand with the de facto standard.   
Browser vendors could learn from this.

The whole point is to not to be able to execute existing code that  
relies on behaviors that are not well defined between de jure and de  
facto standards.  As a web author, I would find it extremely useful,  
which is the whole point, because it does not encourage blind use of  
behaviors with broken definitions.  Browsers only written with  
supposed compatibility for end users in mind do encourage blind use  
of behaviors with broken definitions, which is why we are where we  
are after so many years and efforts in the standards arena.  In  
reality, it is fairly easy to avoid such behaviors if they are  
flagged for you.

The normal users would normally run in mode 1, or possibly 2 in  
unusual circumstances.  Never 3 unless gathering information to  
report a broken web site.

There is no one to assign responsibility for current messes other  
than the browser vendors and if they want better-standardized  
content, they need to provide tools with more integrity that holds  
the content for web authors to a higher standard than it generally  
allows normal users to execute.  Standardization efforts rise or fall  
on the efforts of browser vendors.  It is quite clear how we got here.

Ray Whitmer
Received on Wednesday, 7 December 2005 21:58:56 UTC

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