fails:Regexp#encoding returns an Encoding object
fails:Regexp#encoding defaults to US-ASCII if the Regexp contains only US-ASCII character
fails:Regexp#encoding returns US_ASCII if the 'n' modifier is supplied and only US-ASCII characters are present
fails:Regexp#encoding returns ASCII-8BIT if the 'n' modifier is supplied and non-US-ASCII characters are present
fails:Regexp#encoding defaults to UTF-8 if \u escapes appear
fails:Regexp#encoding defaults to UTF-8 if a literal UTF-8 character appears
fails:Regexp#encoding returns UTF-8 if the 'u' modifier is supplied
fails:Regexp#encoding returns Windows-31J if the 's' modifier is supplied
fails:Regexp#encoding returns EUC_JP if the 'e' modifier is supplied
fails:Regexp#encoding upgrades the encoding to that of an embedded String
fails:Regexp#encoding ignores the encoding and uses US-ASCII if the string has only ASCII characters
fails:Regexp#encoding ignores the default_internal encoding
