Begins a process to update the elements (nodes) of an SVG document.
The user can modify the elements of an SVG document using EnumerateElements and update the node's elements or attributes.
After modifying the values of an SVG document using SvgNodeHandle, it may be necessary to re-calculate the document flat, render optimization and bounding rectangles (refer to SVG Size, Bounds and Flat more information). Therefore, it is best to call BeginUpdate before making any updates to the document and to call EndUpdate when finished. The engine will check during EndUpdate whether any internal state values need to be re-calculated and updated as necessary.
BeginUpdate increments an internal counter and EndUpdate decrements it. When the counter reaches 0 again, the document is updated. Therefore, the user can chain calls to BeginUpdate / EndUpdate pair and the update will only occur once at the end.