Document CGI.build_form

Author: Ary Borenszweig

src/cgi.cr

@@ -90,12 +90,27 @@ module CGI
     end
   end
 
+  # Builds a CGI form.
+  #
+  # The yielded object has an `add` method that accepts two arguments,
+  # a key (String) and a value (String or Nil). Keys and values are escaped
+  # using `CGI#escape`.
+  #
+  # ```
+  # params = CGI.build_form do |form|
+  #   form.add "color", "black"
+  #   form.add "name", "crystal"
+  #   form.add "year", "2012 - today"
+  # end
+  # params #=> "color=black&name=crystal&year=2012%20-%20today"
+  # ```
   def self.build_form
     form_builder = FormBuilder.new
     yield form_builder
     form_builder.to_s
   end
 
+  # :nodoc:
   struct FormBuilder
     def initialize
       @string = StringIO.new