Extended elements

SVG Extend propose various extension to SVG among which elements extension. Elements are extended through the is attribute and gain some new attributes to deal with the extension.

Name	`is` value	Extend	New Attributes
ngon	`n-gon`	`<path>`, `<polygon>`, `<polyline>`	`cx`, `cy`, `r`, `vertex`, `density`
star	`n-star`	`<path>`, `<polygon>`, `<polyline>`	`cx`, `cy`, `r`, `vertex`