[Feature #18788] [DOC] String options to `Regexp.new`

Co-Authored-By: Janosch Müller <janosch.mueller@betterplace.org>

doc/regexp.rdoc

@@ -620,6 +620,11 @@ Options may also be used with <tt>Regexp.new</tt>:
     Regexp.new("abc # Comment", Regexp::EXTENDED)             #=> /abc # Comment/x
     Regexp.new("abc", Regexp::IGNORECASE | Regexp::MULTILINE) #=> /abc/mi
 
+    Regexp.new("abc", "i")           #=> /abc/i
+    Regexp.new("abc", "m")           #=> /abc/m
+    Regexp.new("abc # Comment", "x") #=> /abc # Comment/x
+    Regexp.new("abc", "im")          #=> /abc/mi
+
 == Free-Spacing Mode and Comments
 
 As mentioned above, the <tt>x</tt> option enables <i>free-spacing</i>

re.c

@@ -3665,6 +3665,11 @@ str_to_option(VALUE str)
  *
  *  Optional argument +options+ is one of the following:
  *
+ *  - A String of options:
+ *
+ *      Regexp.new('foo', 'i')  # => /foo/i
+ *      Regexp.new('foo', 'im') # => /foo/im
+ *
  *  - The logical OR of one or more of the constants
  *    Regexp::EXTENDED, Regexp::IGNORECASE, and Regexp::MULTILINE:
  *