What about requirements in ETSI deliverables?
The requirements shall be mentioned only in normative clauses and deliverables (European Standard (EN), ETSI Standard (ES), Technical Specification (TS) and Group Specification (GS)).
The ETSI Drafting Rules (EDRs) specify that ETSI Technical Reports (TRs), ETSI Guides (EGs), Special Reports (SRs) and Group Reports (GRs) shall be entirely informative, this means that the verbal forms "shall" and "must" or any other wording which would imply a requirement (i.e. "has to", "have to" and "required to") shall be avoided in all parts of the deliverable.
Their verbs should be limited to the simple indicative tense, without using auxiliaries such as shall/must.
See clause 3 of the ETSI Drafting Rules for further information.