But a "mandatory" is so clear that it actually requires no further inquiry.
However, the quoted wording – which, as mentioned, is not clarified in the reasoning of the plan – is incomprehensible on a "it can't get any worse" level: 2. it speaks of a building length for which it is stipulated that the building depth must be equal to the building width. Aha ????? For two of these three terms, the content must already be the same, since there are only two dimensions in total. The lawyer doesn't dismiss this himself; he sends his trainee to do it. Whether it is indefinite or incomprehensible, he can choose. and 1. this is supposed to apply if the second full storey is not constructed in an attic – again without any comprehensibility, even in the reasoning of the plan. Normally, such wording in a sloped site – which we do not have here – indicates that a second full storey can already be created as a basement. Or it means the upper floor of an "Anstattvilla" (alternative villa) not called "attic" due to the lack of slants. Nevertheless, the municipality here fails to provide the derivation as to why a square floor plan should then be required (and I cannot imagine a legally sound reasoning for that either). The reasoning of a development plan misses its sense and purpose if it cannot dispel the impression of arbitrariness of the requirements. This development plan will be challenged without difficulty by a junior lawyer (or divorce lawyer). Such administrative acts serve no one, certainly not the legal certainty of building applicants. Presumably, the sentence served to appease a factionless troublemaker, to bring the consultation to an end before midnight :-(