The tag implication #45505 helmet_only -> mostly_nude has been rejected.
Reason: Helmets are considered armor, which is considered clothing when a character is wearing it. In order to have the helmet_only tag, the character must be wearing the helmet, thus making it clothing.
Implicating headgear_only to mostly_nude is not possible. Headsets implicate headgear, yet headsets are not clothing, so a character with only a headset would be considered nude instead. Headdresses likewise implicate headgear and are not always clothing since the tag may be used for minimal ornamental jewelry worn on the head (see: Ankha being commonly tagged with headdress).
Off the top of my head, I cannot think of a helmet being worn that wouldn't constitute clothing by the definition of the armor tag.
EDIT: It may also be prudent for helmet_only to implicate clothing since armor is being worn, making it clothing.
EDIT: The tag implication helmet_only -> mostly_nude (forum #340968) has been rejected by @slyroon.
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