With the AICC working on a new specification to update the existing use of the CMI data model and replace the ageing (but still popular!) HACP it seems like a good opportunity to fix the concept of launch via a web browser to harmonise learning technology standards with best practice in mainstream applications. By the way, if you are curious HACP is defined in the 1993 document: [CMI001] CMI Guidelines for Interoperability AICC.
The Learning Management System (LMS) typically does the launch by creating a special page that is delivered to the user's web browser containing a form (or a naked hyperlink with query parameters) to trigger the activity in a remote system. There are some subtle things going on here because best practice in HTML has been based on the assumption that the server that generated the form is the one that will receive the submission whereas our community tends to rely on cross-site form submission (XSFS perhaps?).
Anyway, you can read my recommendation to the AICC in the open forum created by them to discuss the CMI-5 draft specification. And of course, if you haven't had a look yet I'd encourage you to have a quick look over the specification yourself. The more people review and comment on these documents the better.
The topic I just started with my new proposal on how the LMS should launch a learning activity in future. I'm recommending that the POST method is used with GET supported for backwards compatibility only so if you support AICC standards please read and review my proposal because you might have to do some work on your launch code to support CMI-5 if my proposal is accepted.
Link: CMI-5 Forum Home Page
The home page of the AICC CMI-5 public forum, see all threads about the proposed specification here. Note that only registered users can see the interactive specification viewer in the forums but there is a general public download on the main CMI-5 page:
Link: CMI-5 Home Page
You can download the full specification as a PDF from here.