Currently the TP model uses old types EL_TYPE_DEF and TYPE_DEF_XXX (i.e. TYPE_DEF_BOOLEAN etc) to represent meta-typing for expressions. See https://specifications.openehr.org/releases/PROC/latest/task_planning.html#_plan_data_context
These meta-types are no longer in use in the Expression Language, and in any case, we can make TP independent from the EL by using BMM meta-types instead, as the BMM has been augmented now to represent BMM_VALUE, BMM_TYPE and specific sub-meta-types e.g. BMM_STRING etc. See e.g. such types used in definition of String and Integer enumeration meta-types.