The *dekalog which defines Tcl is completely recursive, in that command substitution is performed over words (7. Command Substitution) and over the completely-substituted command (2. Evaluation).
It is useful to consider incompletely recursive Tcl, where the invariant in (2. Evaluation, 'These substitutions are performed in the same way for all commands') was abrogated.
One reason to consider this is that the universality of application seems to be surplus to requirements... it seems that it restates in (2.) what is already strongly implied by (7.) through (2.) As post-Euclidean Tcl suggests, there may be virtue in reconsidering this kind of duplication and over-constraint.
Another reason to consider abrogating the universal-application sub-rule is that it permits one to do interesting things, by making Tcl incompletely recursive.