Ruby unless/case

unless 条件 then
　文
end

case 比較したいオブジェクト
 when 値1 then
  文1
 when 値2 
  文2
 when 値3
  文3
 else
  文4
 end

case.rb
tags = [ "A", "IMG", "PRE"]
tags.each do |tagname|
 case tagname
when "P", "A", "I", "B", "BLOCKQUOTE"
 puts "#{tagname} has child"
when "IMG", "BR"
puts "#{tagname} has no child"
else
puts "#{tagname} can not be used"
 end
end

> ruby case.rb
A has child, IMG has no child, PRE can not be used