The Commission contrasts "clearly stating the subject matter" with "taking the form of a draft legal act". I do not think that a draft legal act is necessary. I do think that aside of the subject matter and objectives, the initiative should identify:

a) Under which power and procedure legislation should be initiated
b) How the act would implement the objectives set out in the treaties with regard to that power

Because these are formal requirements for admissibility. A statement on subsidiarity should also be included.

I'm not sure that this is necessary. If the petitioners can't draft a clear text, then they shoot themselves in the foot and the Commission can interpret it the way they like.

_{*Lunatic*, n.
One whose delusions are out of fashion.}

It should be sufficient to set out the formal objectives of a proposal - e.g. to promote more equal contributions to climate change mitigation and an outline of how a carbon tax mechanism would achieve this.  Otherwise you could have numerous carbon tax ECIs all proposing slightly different mechanisms with none achieving the necessary level of sigs even if all of them, in aggregate, do.

notes from no w here