The activity of providing an on-going description of what one is doing, how and why as a means of teaching another how to carry out an activity
An ethnomethodological take on the status of rules would be that to know a rule and to follow a rule basically means knowing what to do and how to execute it. Following on from this, knowing a procedure and being able to follow it, does not mean having learned it from a process diagram but instead being able to carry out the procedure in practical application. In our example of XP software development, workers as the situation demands (often in paired programming situations) will sometimes give a running commentary of what they are doing, why, to the other half of the pair. This is a technique used particularly by an experienced developer, when showing an inexperienced person how to carry out some activity. This showing by doing may also be a more general technique used in pair programming to enhance the availability of actions (i.e. accompany what can be seen with an extra description) and so promote better understanding for collaboration.
In this instantiation of XP we see the use of 'running commentary' as a commonplace practice that is used to teach, show, and share details of on-going work. The explicit organisation of 'revolving' pair programming promotes the sharing of knowledge and expertise and cooperative problem solving through the process and practices of work. If one of the pair seeks to communicate how to do something, how they are carrying something out etc., this is a sensible technique for achieving this. This is intended foster better cooperation and communication of knowledge than other methods, as for example, showing others what to do is part of the getting the day-to-day work done whereas in other situations workers may have to stop their work to help in the work of others.