For more details, see RFC 6570.

^([^\x00-\x20\x7f"'%<>\\^`{|}]|%[0-9A-Fa-f]{2}|{[+#./;?&=,!@|]?((\w|%[0-9A-Fa-f]{2})(\.?(\w|%[0-9A-Fa-f]{2}))*(:[1-9]\d{0,3}|\*)?)(,((\w|%[0-9A-Fa-f]{2})(\.?(\w|%[0-9A-Fa-f]{2}))*(:[1-9]\d{0,3}|\*)?))*})*$ \ \_____________/ \\____________/ \\__________________/ \__________________/ /\________________/ / \_________________________________________________________________/ // \ pct-encoded / \ operator \\ varchar varchar / modifier-level4 / varspec // \______________________________________/ \ \\________________________________________/ / // literals \ \ varname / // \ \_________________________________________________________/ // \ \ varspec // \ \____________________________________________________________________________________________________________________________// \ variable-list / \_________________________________________________________________________________________________________________________________________/ expression