A CML comment may appear anywhere in a python file and may occupy one or many lines. The 'cml' and 'cml+' literals are what distinguish the CML comments from the others. The version is introduced for the future if CML is evolving.
The record type defines what will be done on the graphics pane. For example the record type CC can stand for Custom Color and expect parameters which describe the custom background and foreground colors.
Sometimes the only one record of a CML comment is required as in the CC case. The CC CML comment appears as a leading comment and affects the item below. In some other cases a couple of records is required. For example, if it is grouping of the graphics items then the beginning and the end need to be marked. So two records will appear at the appropriate places in the source code.
The last thing to say here is that the chosen format is so simple and human readable that even emacs users will be able to read the CML comments essential content.