missing functionality for svg <use> elements

[plsnk]

With the ImageSVG functionality, is not displayed correctly.

location of missing functionality startSVGElementHandler and endSVGElementHandler.

behavior in version 6.6.5

• objects outside <defs> elements can not be referenced with <use> since they are not stored in array $svgdefs.
• $svgdefs does not contain child elements with id attributes set.

additional info

• currently the structure does not allow for elements to be stored as child element and independently being referenced.
• a <use> element within a recursive call from a <use> can cause issues when addressing the points above.