mechanize：Mechanize::Form::ImageButton#x, #y

everyday Ruby

以下のような HTML で

<html>
<head>
<title>form test</title>
</head>
<body>

<form method="get" action="cgi/foo00.cgi" name="form1">
  <input type="image" src="foo1.png" name="image1" />
  <input type="image" src="foo2.png" name="image2" />
</form>

</body>
</html>
>> require 'mechanize'
=> true
>> agent = Mechanize.new
=> #<Mechanize:0xb74c45ac ...
>> page = agent.get('http://127.0.0.1:8080/test19_form.html')
=> #<Mechanize::Page
  ...
>> f = page.form('form1')
=> #<Mechanize::Form
  ...
>> f.buttons
=> [#<Mechanize::Form::ImageButton:0xb74b8194 @name="image1", @y=nil, @x=nil, @value=nil, @node=#<Nokogiri::XML::Element:0x..fdba5c174 name="input" attributes=[#<Nokogiri::XML::Attr:0x..fdba5a5e0 name="type" value="image">, #<Nokogiri::XML::Attr:0x..fdba5a5d6 name="src" value="foo1.png">, #<Nokogiri::XML::Attr:0x..fdba5a5cc name="name" value="image1">]>>, #<Mechanize::Form::ImageButton:0xb74b7ff0 @name="image2", @y=nil, @x=nil, @value=nil, @node=#<Nokogiri::XML::Element:0x..fdba5c124 name="input" attributes=[#<Nokogiri::XML::Attr:0x..fdba5897a name="type" value="image">, #<Nokogiri::XML::Attr:0x..fdba58970 name="src" value="foo2.png">, #<Nokogiri::XML::Attr:0x..fdba58966 name="name" value="image2">]>>]
>> f.buttons.size
=> 2
>> f.buttons[0].x
=> nil
>> f.buttons[0].y
=> nil

設定・活用されるタイミングってあるのか？？？