diff --git a/lib/uri/common.rb b/lib/uri/common.rb
index 17bea9e97a..ac72a9ebc2 100644
--- a/lib/uri/common.rb
+++ b/lib/uri/common.rb
@@ -185,23 +185,13 @@ module URI
     RFC3986_PARSER.parse(uri)
   end
 
+  # Merges the given URI strings +str+
+  # per {RFC 2396}[https://www.rfc-editor.org/rfc/rfc2396.html].
   #
-  # == Synopsis
+  # Each string in +str+ is converted to an
+  # {RFC3986 URI}[https://www.rfc-editor.org/rfc/rfc3986.html] before being merged.
   #
-  #   URI::join(str[, str, ...])
-  #
-  # == Args
-  #
-  # +str+::
-  #   String(s) to work with, will be converted to RFC3986 URIs before merging.
-  #
-  # == Description
-  #
-  # Joins URIs.
-  #
-  # == Usage
-  #
-  #   require 'uri'
+  # Examples:
   #
   #   URI.join("http://example.com/","main.rbx")
   #   # => #<URI::HTTP http://example.com/main.rbx>
@@ -246,7 +236,7 @@ module URI
   #   URI.extract("text here http://foo.example.org/bla and here mailto:test@example.com and here also.")
   #   # => ["http://foo.example.com/bla", "mailto:test@example.com"]
   #
-  def self.extract(str, schemes = nil, &block)
+  def self.extract(str, schemes = nil, &block) # :nodoc:
     warn "URI.extract is obsolete", uplevel: 1 if $VERBOSE
     DEFAULT_PARSER.extract(str, schemes, &block)
   end
@@ -283,7 +273,7 @@ module URI
   #     p $&
   #   end
   #
-  def self.regexp(schemes = nil)
+  def self.regexp(schemes = nil)# :nodoc:
     warn "URI.regexp is obsolete", uplevel: 1 if $VERBOSE
     DEFAULT_PARSER.make_regexp(schemes)
   end
@@ -340,16 +330,38 @@ module URI
   #   and then to encoding +enc+.
   #
   # In either case, the returned string has forced encoding Encoding::US_ASCII.
-  #
   def self.encode_www_form_component(str, enc=nil)
     _encode_uri_component(/[^*\-.0-9A-Z_a-z]/, TBLENCWWWCOMP_, str, enc)
   end
 
-  # Decodes given +str+ of URL-encoded form data.
+  # Returns a string decoded from the given \URL-encoded string +str+.
   #
-  # This decodes + to SP.
+  # The given string is first encoded as Encoding::ASCII-8BIT (using String#b),
+  # then decoded (as below), and finally force-encoded to the given encoding +enc+.
+  #
+  # The returned string:
+  #
+  # - Preserves:
+  #
+  #   - Characters <tt>'*'</tt>, <tt>'.'</tt>, <tt>'-'</tt>, and <tt>'_'</tt>.
+  #   - Character in ranges <tt>'a'..'z'</tt>, <tt>'A'..'Z'</tt>,
+  #     and <tt>'0'..'9'</tt>.
+  #
+  #   Example:
+  #
+  #     URI.decode_www_form_component('*.-_azAZ09')
+  #     # => "*.-_azAZ09"
+  #
+  # - Converts:
+  #
+  #   - Character <tt>'+'</tt> to character <tt>' '</tt>.
+  #   - Each "percent notation" to an ASCII character.
+  #
+  #   Example:
+  #
+  #     URI.decode_www_form_component('Here+are+some+punctuation+characters%3A+%2C%3B%3F%3A')
+  #     # => "Here are some punctuation characters: ,;?:"
   #
-  # See URI.encode_www_form_component, URI.decode_www_form.
   def self.decode_www_form_component(str, enc=Encoding::UTF_8)
     _decode_uri_component(/\+|%\h\h/, str, enc)
   end