def self.merge_attrs(to, from)
from['id'] = Precompiler.filter_and_join(from['id'], '_') if from['id']
if to['id'] && from['id']
to['id'] << '_' << from.delete('id').to_s
elsif to['id'] || from['id']
from['id'] ||= to['id']
end
from['class'] = Precompiler.filter_and_join(from['class'], ' ') if from['class']
if to['class'] && from['class']
from['class'] = (from['class'].to_s.split(' ') | to['class'].split(' ')).sort.join(' ')
elsif to['class'] || from['class']
from['class'] ||= to['class']
end
from_data = from['data'].is_a?(Hash)
to_data = to['data'].is_a?(Hash)
if from_data && to_data
to['data'] = to['data'].merge(from['data'])
elsif to_data
to = Haml::Util.map_keys(to.delete('data')) {|name| "data-#{name}"}.merge(to)
elsif from_data
from = Haml::Util.map_keys(from.delete('data')) {|name| "data-#{name}"}.merge(from)
end
to.merge!(from)
end