关于"unable to open editor, unknown ID"的错误

回答
Have you specified the 'icon' attribute in the plugin extension editor for your editor? It may sound strange, but the icon attribute is required if you supply your own class in the 'class' attribute to implement the IEditorPart interface.

Well, the icon itself does not need to exist, but the 'icon' attribute's field must not be empty. Without the icon defined, your editor never gets into the editor registry when the plugin extensions are read, so an attempt later to retrieve this editor by its id fails, even though the editor ID is correct.