Nowadays Learning Management Systems (LMS) are not restricted to distant uses. Nevertheless, the pedagogical expressiveness of designed courses is strongly dependent on the teacher's knowledge and expertise about the targeted platform. The funded GraphiT project aims to help teachers in focusing on the specification of pedagogically sound and technically executable learning designs. To this end, we propose to support teachers by providing an LMS-specific Visual Instructional Design Language (VIDL). This paper proposes a specific LMS- centered approach for raising the pedagogical expressiveness of its implicit learning design semantics. We discussed, in accordance to the activity theory, how the LMS low-level parameterizations could be abstracted in order to build higher- level building blocks. Based on the Moodle application, we present and illustrate our approach by formalising the abstract syntax of a Moodle-dedicated VIDL.