We are rewriting this. Right now, the best specification of an ‘expression language’ is in the BMM, Expression section - [https://specifications.openehr.org/releases/LANG/latest/bmm.html#_expressions].
This is the new meta-model. We will probably update the EL spec to be one possible concrete language, which probably won’t be much different from what is there now, but the statement parts will disappear I think (if/then/else etc), and there will be the possibility to write agent (lambda) expressions. The main area not finalised yet is ‘predicates’, which currently includes ‘attached()’ and ‘defined()’, but in theory could include a whole path-based sub-language like Xpath, where you could write predicates based on number of child objects, or the values in some child object. If we do that, we’ll specify that as a separate sub-language.
In the Task Planning group, we are working on decision structures / statements etc in a clinical Decision language which will have a draft up soon.