[svgwg] Third parameter of arc in path data should allow signed numbers (#750)

dalboris has just created a new issue for https://github.com/w3c/svgwg:

== Third parameter of arc in path data should allow signed numbers ==
Hi everyone,

As I'm currently writing a parser for SVG path data, I'm able to provide a new pair of eyes for the new grammar definition introduced in SVG 2. Disclaimer: I'm not a grammar specialist, but I did study those things at University a few years back, so hopefully I'm not too rusty.

I am now reasonably familiar with the original SVG 1.1 grammar:

https://www.w3.org/TR/SVG11/paths.html#PathDataBNF

The one currently drafted in:

https://svgwg.org/svg2-draft/paths.html#PathDataBNF

And I have read the following threads to get a sense of the history and rationale of some of the modifications:

https://github.com/w3c/svgwg/issues/335
https://github.com/w3c/svgwg/issues/331
https://github.com/w3c/svgwg/issues/286
https://github.com/w3c/svgwg/issues/325

Overall, I think the SVG 2 draft grammar reads much better than the SVG 1.1 grammar, thank you for that! I may suggest minor tweaks later to improve readability, but for now a more serious issue. I think the following:

```
elliptical_arc_argument::=
    number comma_wsp? number comma_wsp? number comma_wsp
    flag comma_wsp? flag comma_wsp? coordinate_pair
```

should be:

```
elliptical_arc_argument::=
    number comma_wsp? number comma_wsp? coordinate comma_wsp
    flag comma_wsp? flag comma_wsp? coordinate_pair
```

In other words, the third parameter of an arc should be `coordinate` rather than `number` (it can be negative). The original SVG 1.1 grammar was the following:

```
elliptical-arc-argument:
    nonnegative-number comma-wsp? nonnegative-number comma-wsp? 
        number comma-wsp flag comma-wsp? flag comma-wsp? coordinate-pair
```

This seems an unintentional mistake, as I haven't seen this discussed, but maybe I missed it.

Cheers,
Boris

Please view or discuss this issue at https://github.com/w3c/svgwg/issues/750 using your GitHub account

Received on Monday, 18 November 2019 00:56:12 UTC