#149 Chemspider 3D images cannot be exported

[David R Newman]

When you export a notebook, Chemspider 3D images are not properly exported. This is because they rely on external javascript and CSS. I brief test to see if these could just be added to the export header was unsuccessful, so there may be other issues that need resolving to make this work. Ideally, the Chempsider CSS and JavaScript files should be included in the export, so the 3D images work when offline.