Re: [xsl] Trimming (formatting-only) leading tabs/spaces from XSLT - issues?

Subject: Re: [xsl] Trimming (formatting-only) leading tabs/spaces from XSLT - issues?
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Tue, 07 Jun 2011 11:59:02 -0400

You are entirely correct that this is an emotional issue. Paradoxically, people get most upset when what seems like "correct" and "common sense" to them is ignored or defied in favor of some other method whose logic is obscure. (For whatever reason, it seems people have less patience with unknowns they believe to be knowable and controvertible than they do with the apparently unknowable and incontrovertible. And machines are supposed to be knowable.)

So the first rule is, make it possible to turn off the behavior, and if other features depend on it, make those dependencies very clear.

On the issue of whitespace in XML, this is one of the most vexing areas, largely because many people don't know what the rules are -- but (and, or) do have their own notions of what's right. The rules you enumerate are a start, except where they blur (such as #3 -- in the XSLT namespace, for example, the 'text' element is sacrosanct, but in the TEI namespace it follows rule #1). Trouble will start with the blurry cases if it hasn't already.

Accordingly, I think the second rule is to be very conservative.

In XSLT, I think this means you can follow the specs regarding where whitespace is not significant (i.e. it is significant except for whitespace-only text nodes outside xsl:text).

In XML (and SGML, including SGML-conformant HTML), I think this means you can follow a schema -- significant whitespace is anywhere character data is permitted. Regrettably, this means that all whitespace (outside tags) is significant when there is no schema. (Whether you can take a schema to be implicit when it is not given is another problem.)

Whether XML (or HTML) fragments embedded in XSLT can be taken to reference a schema depends, I'm afraid, on the XSLT: it won't always be true. Conservatively, we might say it's never definitively true except when a schema is specifically assigned using xsl:import-schema and xsl:result-document/@validation='strict'. But I suppose an application might also let a user declare such a binding by other means.

In plain text, I think all bets are off, in the general case. Variants of plain text that conform to particular specifications may constitute exceptions, and maybe you could define such a spec for a "smart" plain text format. But as you say, it wouldn't be perfect.

Finally, I think it's important to distinguish between whitespace handling in tag-formatting applications from the way whitespace may, or may not, be collapsed, re-flowed or munged for display in a receiving application. These are two different issues that are frequently confused. The fact that some tag-formatting applications may (usefully) reformat whitespace in some places where it is not entirely stripped -- perhaps on the grounds that receiving applications will be doing likewise, so it doesn't matter -- makes for another set of troublesome blurry cases.

My $0.02.


On 6/7/2011 10:26 AM, Philip Fearon wrote:
This wouldn't ever be perfect, but there's a large set of rules that
could be used to determine formatting-only whitespace. The following
set is a distilled version:
From the XML context:
1. Outside mixed-content
2. Outside where xsl:space "preserve" is in scope
3. Outside defined elements such as 'pre' and 'text'
4. If it precedes an attribute name beginning a new line
5. If it precedes an attribute value on a new line
From text context:
4. Where the number of characters found are (within a defined margin)
is consistent with the current nesting-level - a pattern can normally
be established
5. Where irregular leading whitespace is found on consecutive lines in
a node value

The approach would be progressive where, on first load a minimal set
of 'obvious' formatting is removed, then further options provided to
the developer that steadily impose a more rigorous filtering

Phil Fearon

-- ====================================================================== Wendell Piez mailto:wapiez@xxxxxxxxxxxxxxxx Mulberry Technologies, Inc. 17 West Jefferson Street Direct Phone: 301/315-9635 Suite 207 Phone: 301/315-9631 Rockville, MD 20850 Fax: 301/315-8285 ---------------------------------------------------------------------- Mulberry Technologies: A Consultancy Specializing in SGML and XML ======================================================================

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