Hi, I'd like to share one thing.
We use chart.svg() result to convert it to .png image via librsvg
Sometimes it output blank image, in some other cases it produces normal png image.
I've found cause
sometimes id starts with digit, other time with letter
id value cannot be uuid (xml id attribute value must be xml name - can't start width digit, see http://www.w3.org/TR/xml/#sec-attribute-types)
I've removed id's from svg completely, it solved my problem (empty image when pass svg to png via rsvg or imagemagick)
Could you please review and fix this?