From: Maël Nison <nison.mael@gmail.com>

Date: Tue, 25 Jun 2013 15:58:02 +0200

Message-ID: <CANiF4iBJwMVOWjCvME6SKU_05k8SVAZ7=sQY97_ue9SVtokotg@mail.gmail.com>

To: "Tab Atkins Jr." <jackalmage@gmail.com>

Cc: www-style list <www-style@w3.org>

Date: Tue, 25 Jun 2013 15:58:02 +0200

Message-ID: <CANiF4iBJwMVOWjCvME6SKU_05k8SVAZ7=sQY97_ue9SVtokotg@mail.gmail.com>

To: "Tab Atkins Jr." <jackalmage@gmail.com>

Cc: www-style list <www-style@w3.org>

Thanks. However, I still don't understand something : *We disallowed division by units at this level, so we can determine whether the math expression is valid at parse-time, since all divisions have only pure-numeric expressions for their right operand.* Why can't we have a division by units and a parse-time validation of the expression ? For example, "100px/(43px - 43px)" is invalid and can as easily be detected as such than "100px/(43 - 43)" (since both of them are absolute). It seems to me that the main problem is about relative units such as percentages or em ("100px / 100%" could be invalid at runtime), or expression derivating from one of those units ("100px / (100px - 100%)"). Also, why should the two operands have the same unit ? Can't the right operand be coerced into the left operand unit ? On 24 June 2013 03:37, Tab Atkins Jr. <jackalmage@gmail.com> wrote: > On Fri, Jun 21, 2013 at 3:18 AM, Maël Nison <nison.mael@gmail.com> wrote: > > Hi, > > > > I've recently come across a use case where the modulus operator would > have > > been useful[1], so I was wondering what were the reason which led to its > > eviction from the current spec. I have been able to find the following > > discussion[2], but I'm not sure to fully understand the argument : > > > > 1. We drop the 'mod' operator since it only makes sense when > > both operands have the same units. > > > > In my fiddle, you can see that I'm using a 'px' modulus on a percentage, > and > > I think it makes perfect sense after converting the percent into a pixel > > unit (which is probably delayed up to the rendering ?). > > > > Am I missing something ? > > > > [1] http://jsfiddle.net/bBESS/4/ > > [2] http://lists.w3.org/Archives/Public/www-style/2010Jul/0442.html > > The reasoning in that email is somewhat truncated. A more expanded > version would be: > > 1. The mod operator, like the / operator, is invalid when the right > operand is 0. > 2. We disallowed division by units at this level, so we can determine > whether the math expression is valid at parse-time, since all > divisions have only pure-numeric expressions for their right operand. > 3. mod requires both sides to be the same unit; since we disallow mod > by units (by the same reasoning as /), this leaves us with mod only > working between two numbers, which is of extremely minimal utility. > 4. Thus, we should exclude mod for now, and add it in when we allow > full unit algebra. > > ~TJ > -- Maël Nison JS Github hipster, Assistant C++ chez EpitechReceived on Tuesday, 25 June 2013 13:58:51 UTC

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