oh ok, in app/models/status.rb:

'''
before_create :set_locality
'''

and then in there

'''
def set_locality
if account.domain.nil? && !attribute_changed?(:local_only)
self.local_only = marked_local_only?
end
end
'''

and a couple paragraphs above that:

'''
def marked_local_only?
# match both with and without U+FE0F (the emoji variation selector)
/#{local_only_emoji}\ufe0f?\z/.match?(content)
end

def local_only_emoji
'👁'
end
'''