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Re: [css-style-attr] SVG WG comments on CSS Styling Attributes Level 1

From: Zack Weinberg <zweinberg@mozilla.com>
Date: Tue, 9 Feb 2010 16:30:23 -0800
To: Chris Lilley <chris@w3.org>
Cc: www-style@w3.org
Message-ID: <20100209163023.70555f7b@trurl>
Chris Lilley <chris@w3.org> wrote:
> 
> These comments relate to CSS Styling Attributes Level 1, W3C Working
> Draft 21 January 2010 from the perspective of SVG.

I can only comment on one of your points, and I do not speak for the
committee.

> This appears to allow unitless values ('number'), for those properties
> defined to accept them, and scientific notation, for those properties
> defined to accept it. However, that depends on the exact syntax of the
> NUMBER token, which is apparently defined in a printed book.
> 
> [FLEX]
>     "Flex: The Lexical Scanner Generator", Version 2.3.7, ISBN
> 1882114213.

I believe this is the citation appearing at the beginning of section
G.2?  If so, I think you have misunderstood the citation; my reading is
that that reference only defines the _notation_ being used immediately
below to define the tokenization rules.

The actual definition of NUMBER is given by these lines from section
G.2:

num		[0-9]+|[0-9]*"."[0-9]+

{num}           { return NUMBER; }

Thus, a NUMBER is always unitless (unitful numbers are DIMENSION
tokens, syntactically {num}{ident}) and cannot (in CSS2.1 as it is
today) be written in scientific notation.

Mozilla's CSS parser has a special mode for all styles loaded from SVG,
including inline styles on SVG-namespace elements.  In that mode the
above regular expression becomes

num             ([0-9]+|[0-9]*"."[0-9]+)(e[+-]?[0-9]+)?

(as always, the "e" is case-insensitive).  Numbers with this suffix are
interpreted as scientific notation.  A % or {ident} suffix may follow
the exponent (which converts the token to a PERCENTAGE or DIMENSION
token); I haven't actually read the relevant part of the SVG spec so I
don't know if that's proper, but I imagine it is necessary at least for
DIMENSIONs.

I have been considering a formal proposal to add this to CSS generally,
mainly because it would be nice to get rid of the mode bit.  It might
be too late for CSS Level 2, though.

zw
Received on Wednesday, 10 February 2010 00:30:58 GMT

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