The purpose of this attribute is to allow the author to achieve exact alignment - this is taken from the SVG version 1.1 specification. When using ADE 3.0.86136 on a Windows 7 laptop I get the following. The svg file has been placed directly in the spine of the epub.
note the misalignment down the right hand side. ADE 3.0. The same code when used with Readium, Kobo and Google Player renders
note the alignment down the right hand side. With the Readium, Kobo and Google Player readers the code works?