diff --git a/lib/cgi/core.rb b/lib/cgi/core.rb
index 6a74486..176648b 100644
--- a/lib/cgi/core.rb
+++ b/lib/cgi/core.rb
@@ -755,12 +755,75 @@ class InvalidEncoding < Exception; end
   #
   @@accept_charset="UTF-8" if false # needed for rdoc?
 
-  # Return the accept character set for all new CGI instances.
+  # :call-seq:
+  #   CGI.accept_charset -> encoding
+  #
+  # Returns the default accept character set to be used for new \CGI instances;
+  # see CGI.accept_charset=.
   def self.accept_charset
     @@accept_charset
   end
 
-  # Set the accept character set for all new CGI instances.
+  # :call-seq:
+  #    CGI.accept_charset = encoding
+  #
+  # Sets the default accept character set to be used for new \CGI instances;
+  # returns the argument.
+  #
+  # The argument may be an Encoding object or an Encoding name;
+  # see {Encodings}[https://docs.ruby-lang.org/en/master/language/encodings_rdoc.html]:
+  #
+  #   # The initial value.
+  #   CGI.accept_charset # => "UTF-8"
+  #   CGI.new
+  #   # =>
+  #   #<CGI:0x0000018991db6ae8
+  #    @accept_charset="UTF-8",
+  #    @accept_charset_error_block=nil,
+  #    @cookies={},
+  #    @max_multipart_length=134217728,
+  #    @multipart=false,
+  #    @options={accept_charset: "UTF-8", max_multipart_length: 134217728},
+  #    @output_cookies=nil,
+  #    @output_hidden=nil,
+  #    @params={}>
+  #
+  #   # Set by Encoding name.
+  #   CGI.accept_charset = 'US-ASCII' # => "US-ASCII"
+  #   CGI.new
+  #   # =>
+  #   #<CGI:0x0000018991cf4100
+  #    @accept_charset="US-ASCII",
+  #    @accept_charset_error_block=nil,
+  #    @cookies={},
+  #    @max_multipart_length=134217728,
+  #    @multipart=false,
+  #    @options={accept_charset: "US-ASCII", max_multipart_length: 134217728},
+  #    @output_cookies=nil,
+  #    @output_hidden=nil,
+  #    @params={}>
+  #
+  #   # Set by Encoding object.
+  #   CGI.accept_charset = Encoding::ASCII_8BIT # => #<Encoding:BINARY (ASCII-8BIT)>
+  #   CGI.new
+  #   # =>
+  #   #<CGI:0x0000018991cfc800
+  #    @accept_charset=#<Encoding:BINARY (ASCII-8BIT)>,
+  #    @accept_charset_error_block=nil,
+  #    @cookies={},
+  #    @max_multipart_length=134217728,
+  #    @multipart=false,
+  #    @options={accept_charset: #<Encoding:BINARY (ASCII-8BIT)>, max_multipart_length: 134217728},
+  #    @output_cookies=nil,
+  #    @output_hidden=nil,
+  #    @params={}>
+  #
+  # The given encoding is not checked in this method,
+  # but if it is invalid, a call to CGI.new will fail:
+  #
+  #   CGI.accept_charset = 'foo'
+  #   CGI.new  # Raises ArgumentError: unknown encoding name - foo
+  #
   def self.accept_charset=(accept_charset)
     @@accept_charset=accept_charset
   end