From IMS: "Warwick Bailey, of IMS member Icodeon and Rob Abel of IMS have authored a paper that considers the options for evolving Simple Sequencing. Over the years most have concluded that Simple Sequencing has not been "simple" to implement in SCORM 2004 (the only known implementation of the specification)... The result is an approach that may work both for SCORM (self-paced online instruction) and the new Common Cartridge standard (for instructor-in-the-loop educational content)." Although document is public, access requires a (free) login to the online IMS community. I don't know why IMS requires this; it just breaks links and creates the possibility of unwanted email.