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Re: WOFF spec comments (was Re: Metadata Questions)

From: Chris Lilley <chris@w3.org>
Date: Wed, 10 Nov 2010 21:18:35 +0100
Message-ID: <1796668035.20101110211835@w3.org>
To: "Levantovsky, Vladimir" <Vladimir.Levantovsky@MonotypeImaging.com>
CC: WOFF Working Group FONT <public-webfonts-wg@w3.org>
On Wednesday, November 10, 2010, 9:12:36 PM, Vladimir wrote:

LV> On Wednesday, November 10, 2010 2:52 PM Chris Lilley wrote:

>> On Wednesday, November 10, 2010, 6:03:06 PM, Vladimir wrote:

>> LV> 2. Clause 6, par. 4 (Extended metadata block)
>> LV> The last sentence of the paragraph 4 says "If the metadata block
>> LV> is not followed by a private data block, it MUST either be padded
>> LV> with null bytes to the next 4-byte boundary, or contain no
>> LV> additional padding after the end of the block."
>> LV> It needs to be revised - it seems to say that the last block MUST
>> LV> either be padded or not padded. (which one is true?)

>> I read it as saying there can be at most 0..3 bytes of padding, but no
>> more; and that any padding must only be sufficient to take it to the
>> next longword boundary.

LV> I believe this is what we want it to say, and the part of the sentence "it MUST ... be padded
LV> with null bytes to the next 4-byte boundary" seems to says
LV> exactly that. The presence of "either ... or" kind of throws me
LV> off because it can be read as "If metadata block is not followed
LV> by a private data block, it MUST ... contain no additional
LV> padding", no matter the longword boundary. To be precise, we might
LV> want to remove the second "or" case and add "if necessary, it MUST
LV> be padded with null bytes to the next 4-byte boundary."

I agree.

>> I seem to recall discussion that the OT spec required padding between
>> tables but was silent or ambiguous about padding after the last table.

LV> Yes, this is true, but in practice most of the tools do add
LV> padding for all tables, including the last one. We actually
LV> discuss this in the WOFF spec as well, in the par. 10 of clause 4
LV> in the "Font table padding" (the text that is now normative).
LV> I think that it would be good to be consistent and have the same
LV> requirement applied to all data blocks in the WOFF file.

I agree also.

 Chris Lilley   Technical Director, Interaction Domain                 
 W3C Graphics Activity Lead, Fonts Activity Lead
 Co-Chair, W3C Hypertext CG
 Member, CSS, WebFonts, SVG Working Groups
Received on Wednesday, 10 November 2010 20:18:43 UTC

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