i have been about this for a while (before the Bridget drama even), seeing as priests aren't usually tagged with habit but nuns/priestess are, a habit by definition is a kind of religious uniform with minor differences between the male and female counterpart, even high rank members of the church wear some form of habit (i.e cardinals and popes).
currently the current definition of habit says "Tag is mostly used to describe the headgear associated with nuns.", and the one from coif "A coif /ˈkɔɪf/ is a close fitting cap worn by both men and women".
imo it seems redundant to have two tags that "define" the same concept but are not implied (nor should be), it would be the same as tagging any character wearing a handkerchief and sailor shirt as school_uniform, even if the character is not.
a better definition of the tag could be:
"A religious habit is a distinctive set of garments worn by members of a religious order, usually composed by a capelet, a tunic, dress or scapular, a coif and veil, and sometimes a cloak, use this tag only when the character is wearing the full attire"*
*birettas, mitres, rosaries and other religious items are also usually worn as part of an habit but i think the description would be a bit confusing if we add those in.
for example post #5756801 is a girl dressed as maid, and aside from the character being a nun the only part of the uniform that she's wearing is the coif, so in the context of the image this is not a nun nor is wearing a habit.
post #5716453 is wearing a full set of garments but was not tagged as wearing a habit (but it was tagged as a nun)
post #5731088 has a veil without a coif and aside from the colors there isn't anything that implies this attire is a habit.
also i have seen plenty images of characters that are clearly male being tagged as nuns despite the tag saying "A nun is a woman who has taken special vows committing her to a religious life.", in those cases where a male character is wearing a female habit it should be tagged with crossdressing and habit instead of of using the tag "nun", but there's also maids and butlers, none of which define the sex of the person wearing the uniform even if usually a butler is considered the male counterpart of a maid, which further adds to my confusion of when to tag and not to tag a nun