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diff --git a/include/jsoncons_ext/jsonschema/format_validator.hpp b/include/jsoncons_ext/jsonschema/format_validator.hpp
new file mode 100644
index 0000000..312bf41
--- /dev/null
+++ b/include/jsoncons_ext/jsonschema/format_validator.hpp
@@ -0,0 +1,968 @@
+// Copyright 2020 Daniel Parker
+// Distributed under the Boost license, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+// See https://github.com/danielaparker/jsoncons for latest version
+
+#ifndef JSONCONS_JSONSCHEMA_FORMAT_VALIDATOR_HPP
+#define JSONCONS_JSONSCHEMA_FORMAT_VALIDATOR_HPP
+
+#include <jsoncons/config/jsoncons_config.hpp>
+#include <jsoncons/uri.hpp>
+#include <jsoncons/json.hpp>
+#include <jsoncons_ext/jsonpointer/jsonpointer.hpp>
+#include <jsoncons_ext/jsonschema/subschema.hpp>
+#include <cassert>
+#include <set>
+#include <sstream>
+#include <iostream>
+#include <cassert>
+#if defined(JSONCONS_HAS_STD_REGEX)
+#include <regex>
+#endif
+
+namespace jsoncons {
+namespace jsonschema {
+
+    inline
+    bool is_atext( char c)
+    {
+        switch (c)
+        {
+            case '!':
+            case '#':
+            case '$':
+            case '%':
+            case '&':
+            case '\'':
+            case '*':
+            case '+':
+            case '-':
+            case '/':
+            case '=':
+            case '?':
+            case '^':
+            case '_':
+            case '`':
+            case '{':
+            case '|':
+            case '}':
+            case '~':
+                return true;
+            default:
+                return (c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
+        }
+    }
+
+    inline
+    bool is_dtext( char c)
+    {
+        return (c >= 33 && c <= 90) || (c >= 94 && c <= 126);
+    }
+
+    //  RFC 5322, section 3.4.1
+    inline
+    bool validate_email_rfc5322(const std::string& s)
+    {
+        enum class state_t {local_part,atom,dot_atom,quoted_string,amp,domain};
+
+        state_t state = state_t::local_part;
+        std::size_t part_length = 0;
+
+        for (char c : s)
+        {
+            switch (state)
+            {
+                case state_t::local_part:
+                {
+                    if (is_atext(c))
+                    {
+                        state = state_t::atom;
+                    }
+                    else if (c == '"')
+                    {
+                        state = state_t::quoted_string;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::dot_atom:
+                {
+                    if (is_atext(c))
+                    {
+                        ++part_length;
+                        state = state_t::atom;
+                    }
+                    else
+                        return false;
+                    break;
+                }
+                case state_t::atom:
+                {
+                    switch (c)
+                    {
+                        case '@':
+                            state = state_t::domain;
+                            part_length = 0;
+                            break;
+                        case '.':
+                            state = state_t::dot_atom;
+                            ++part_length;
+                            break;
+                        default:
+                            if (is_atext(c))
+                                ++part_length;
+                            else
+                                return false;
+                            break;
+                    }
+                    break;
+                }
+                case state_t::quoted_string:
+                {
+                    if (c == '\"')
+                    {
+                        state = state_t::amp;
+                    }
+                    else
+                    {
+                        ++part_length;
+                    }
+                    break;
+                }
+                case state_t::amp:
+                {
+                    if (c == '@')
+                    {
+                        state = state_t::domain;
+                        part_length = 0;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::domain:
+                {
+                    if (is_dtext(c))
+                    {
+                        ++part_length;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+            }
+        }
+
+        return state == state_t::domain && part_length > 0;
+    }
+
+    // RFC 2673, Section 3.2
+
+    inline
+    bool validate_ipv6_rfc2373(const std::string& s)
+    {
+        enum class state_t{start,expect_hexdig_or_unspecified,
+                              hexdig, decdig,expect_unspecified, unspecified};
+
+        state_t state = state_t::start;
+
+        std::size_t digit_count = 0;
+        std::size_t piece_count = 0;
+        std::size_t piece_count2 = 0;
+        bool has_unspecified = false;
+        std::size_t dec_value = 0;
+
+        for (std::size_t i = 0; i < s.length(); ++i)
+        {
+            char c = s[i];
+            switch (state)
+            {
+                case state_t::start:
+                {
+                    switch (c)
+                    {
+                        case '0':case '1':case '2':case '3':case '4':case '5':case '6':case '7':case '8': case '9':
+                        case 'A':case 'B':case 'C':case 'D':case 'E':case 'F':
+                        case 'a':case 'b':case 'c':case 'd':case 'e':case 'f':
+                            state = state_t::hexdig;
+                            ++digit_count;
+                            piece_count = 0;
+                            break;
+                        case ':':
+                            if (!has_unspecified)
+                            {
+                                state = state_t::expect_unspecified;
+                            }
+                            else
+                            {
+                                return false;
+                            }
+                            break;
+                        default:
+                            return false;
+                    }
+                    break;
+                }
+                case state_t::expect_hexdig_or_unspecified:
+                {
+                    switch (c)
+                    {
+                        case '0':case '1':case '2':case '3':case '4':case '5':case '6':case '7':case '8': case '9':
+                            dec_value = dec_value*10 + static_cast<std::size_t>(c - '0'); // just in case this piece is followed by a dot
+                            state = state_t::hexdig;
+                            ++digit_count;
+                            break;
+                        case 'A':case 'B':case 'C':case 'D':case 'E':case 'F':
+                        case 'a':case 'b':case 'c':case 'd':case 'e':case 'f':
+                            state = state_t::hexdig;
+                            ++digit_count;
+                            break;
+                        case ':':
+                            if (!has_unspecified)
+                            {
+                                has_unspecified = true;
+                                state = state_t::unspecified;
+                            }
+                            else
+                            {
+                                return false;
+                            }
+                            break;
+                        default:
+                            return false;
+                    }
+                    break;
+                }
+                case state_t::expect_unspecified:
+                {
+                    if (c == ':')
+                    {
+                        has_unspecified = true;
+                        state = state_t::unspecified;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::hexdig:
+                {
+                    switch (c)
+                    {
+                        case '0':case '1':case '2':case '3':case '4':case '5':case '6':case '7':case '8': case '9':
+                        case 'A':case 'B':case 'C':case 'D':case 'E':case 'F':
+                        case 'a':case 'b':case 'c':case 'd':case 'e':case 'f':
+                            ++digit_count;
+                            break;
+                        case ':':
+                            if (digit_count <= 4)
+                            {
+                                ++piece_count;
+                                digit_count = 0;
+                                dec_value = 0;
+                                state = state_t::expect_hexdig_or_unspecified;
+                            }
+                            else
+                            {
+                                return false;
+                            }
+                            break;
+                        case '.':
+                            if (piece_count == 6 || has_unspecified)
+                            {
+                                ++piece_count2;
+                                state = state_t::decdig;
+                                dec_value = 0;
+                            }
+                            else
+                            {
+                                return false;
+                            }
+                            break;
+                        default:
+                            return false;
+                    }
+                    break;
+                }
+                case state_t::decdig:
+                {
+                    switch (c)
+                    {
+                        case '0':case '1':case '2':case '3':case '4':case '5':case '6':case '7':case '8': case '9':
+                            dec_value = dec_value*10 + static_cast<std::size_t>(c - '0');
+                            ++digit_count;
+                            break;
+                        case '.':
+                            if (dec_value > 0xff)
+                            {
+                                return false;
+                            }
+                            digit_count = 0;
+                            dec_value = 0;
+                            ++piece_count2;
+                            break;
+                        default:
+                            return false;
+                    }
+                    break;
+                }
+                case state_t::unspecified:
+                {
+                    switch (c)
+                    {
+                        case '0':case '1':case '2':case '3':case '4':case '5':case '6':case '7':case '8': case '9':
+                        case 'A':case 'B':case 'C':case 'D':case 'E':case 'F':
+                        case 'a':case 'b':case 'c':case 'd':case 'e':case 'f':
+                            state = state_t::hexdig;
+                            ++digit_count;
+                            break;
+                        default:
+                            return false;
+                    }
+                    break;
+                }
+                default:
+                    return false;
+            }
+        }
+
+        switch (state)
+        {
+            case state_t::unspecified:
+                return piece_count <= 8;
+            case state_t::hexdig:
+                if (digit_count <= 4)
+                {
+                    ++piece_count;
+                    return digit_count > 0 && (piece_count == 8 || (has_unspecified && piece_count <= 8));
+                }
+                else
+                {
+                    return false;
+                }
+            case state_t::decdig:
+                ++piece_count2;
+                if (dec_value > 0xff)
+                {
+                    return false;
+                }
+                return digit_count > 0 && piece_count2 == 4;
+            default:
+                return false;
+        }
+    }
+
+    // RFC 2673, Section 3.2
+
+    inline
+    bool validate_ipv4_rfc2673(const std::string& s)
+    {
+        enum class state_t {expect_indicator_or_dotted_quad,decbyte,
+                              bindig, octdig, hexdig};
+
+        state_t state = state_t::expect_indicator_or_dotted_quad;
+
+        std::size_t digit_count = 0;
+        std::size_t decbyte_count = 0;
+        std::size_t value = 0;
+
+        for (std::size_t i = 0; i < s.length(); ++i)
+        {
+            char c = s[i];
+            switch (state)
+            {
+                case state_t::expect_indicator_or_dotted_quad:
+                {
+                    switch (c)
+                    {
+                        case '0':case '1':case '2':case '3':case '4':case '5':case '6':case '7':case '8': case '9':
+                            state = state_t::decbyte;
+                            decbyte_count = 0;
+                            digit_count = 1;
+                            value = 0;
+                            break;
+                        case 'b':
+                            state = state_t::bindig;
+                            digit_count = 0;
+                            break;
+                        case 'o':
+                            state = state_t::octdig;
+                            digit_count = 0;
+                            break;
+                        case 'x':
+                            state = state_t::hexdig;
+                            digit_count = 0;
+                            break;
+                        default:
+                            return false;
+                    }
+                    break;
+                }
+                case state_t::bindig:
+                {
+                    if (digit_count >= 256)
+                    {
+                        return false;
+                    }
+                    switch (c)
+                    {
+                        case '0':case '1':
+                            ++digit_count;
+                            break;
+                        default:
+                            return false;
+                    }
+                    break;
+                }
+                case state_t::octdig:
+                {
+                    if (digit_count >= 86)
+                    {
+                        return false;
+                    }
+                    switch (c)
+                    {
+                        case '0':case '1':case '2':case '3':case '4':case '5':case '6':case '7':
+                            ++digit_count;
+                            break;
+                        default:
+                            return false;
+                    }
+                    break;
+                }
+                case state_t::hexdig:
+                {
+                    if (digit_count >= 64)
+                    {
+                        return false;
+                    }
+                    switch (c)
+                    {
+                        case '0':case '1':case '2':case '3':case '4':case '5':case '6':case '7':case '8': case '9':
+                        case 'A':case 'B':case 'C':case 'D':case 'E':case 'F':
+                        case 'a':case 'b':case 'c':case 'd':case 'e':case 'f':
+                            ++digit_count;
+                            break;
+                        default:
+                            return false;
+                    }
+                    break;
+                }
+                case state_t::decbyte:
+                {
+                    if (decbyte_count >= 4)
+                    {
+                        return false;
+                    }
+                    switch (c)
+                    {
+                        case '0':case '1':case '2':case '3':case '4':case '5':case '6':case '7':case '8': case '9':
+                        {
+                            if (digit_count >= 3)
+                            {
+                                return false;
+                            }
+                            ++digit_count;
+                            value = value*10 + static_cast<std::size_t>(c - '0');
+                            if (value > 255)
+                            {
+                                return false;
+                            }
+                            break;
+                        }
+                        case '.':
+                            if (decbyte_count > 3)
+                            {
+                                return false;
+                            }
+                            ++decbyte_count;
+                            digit_count = 0;
+                            value = 0;
+                            break;
+                        default:
+                            return false;
+                    }
+                    break;
+                }
+                default:
+                    return false;
+            }
+        }
+
+        switch (state)
+        {
+            case state_t::decbyte:
+                if (digit_count > 0)
+                {
+                    ++decbyte_count;
+                }
+                else
+                {
+                    return false;
+                }
+                return (decbyte_count == 4) ? true : false;
+            case state_t::bindig:
+                return digit_count > 0 ? true : false;
+            case state_t::octdig:
+                return digit_count > 0 ? true : false;
+            case state_t::hexdig:
+                return digit_count > 0 ? true : false;
+            default:
+                return false;
+        }
+    }
+
+    // RFC 1034, Section 3.1
+    inline
+    bool validate_hostname_rfc1034(const std::string& hostname)
+    {
+        enum class state_t {start_label,expect_letter_or_digit_or_hyphen_or_dot};
+
+        state_t state = state_t::start_label;
+        std::size_t length = hostname.length() - 1;
+        std::size_t label_length = 0;
+
+        for (std::size_t i = 0; i < length; ++i)
+        {
+            char c = hostname[i];
+            switch (state)
+            {
+                case state_t::start_label:
+                {
+                    if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z'))
+                    {
+                        ++label_length;
+                        state = state_t::expect_letter_or_digit_or_hyphen_or_dot;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::expect_letter_or_digit_or_hyphen_or_dot:
+                {
+                    if (c == '.')
+                    {
+                        label_length = 0;
+                        state = state_t::start_label;
+                    }
+                    else if (!((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') ||
+                               (c >= '0' && c < '9') || c == '-'))
+                    {
+                        return false;
+                    }
+                    if (++label_length > 63)
+                    {
+                        return false;
+                    }
+                    break;
+                }
+            }
+        }
+
+        char last = hostname.back();
+        if (!((last >= 'a' && last <= 'z') || (last >= 'A' && last <= 'Z') || (last >= '0' && last < '9')))
+        {
+            return false;
+        }
+        return true;
+    }
+
+    inline
+    bool is_leap_year(std::size_t year)
+    {
+        return (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
+    }
+
+    inline
+    std::size_t days_in_month(std::size_t year, std::size_t month)
+    {
+        switch (month)
+        {
+            case 1: return 31;
+            case 2: return is_leap_year(year) ? 29 : 28;
+            case 3: return 31;
+            case 4: return 30;
+            case 5: return 31;
+            case 6: return 30;
+            case 7: return 31;
+            case 8: return 31;
+            case 9: return 30;
+            case 10: return 31;
+            case 11: return 30;
+            case 12: return 31;
+            default:
+                JSONCONS_UNREACHABLE();
+                break;
+        }
+    }
+
+    enum class date_time_type {date_time,date,time};
+    // RFC 3339, Section 5.6
+    inline
+    bool validate_date_time_rfc3339(const std::string& s, date_time_type type)
+    {
+        enum class state_t {fullyear,month,mday,hour,minute,second,secfrac,z,offset_hour,offset_minute};
+
+        std::size_t piece_length = 0;
+        std::size_t year = 0;
+        std::size_t month = 0;
+        std::size_t mday = 0;
+        std::size_t value = 0;
+        state_t state = (type == date_time_type::time) ? state_t::hour : state_t::fullyear;
+
+        for (char c : s)
+        {
+            switch (state)
+            {
+                case state_t::fullyear:
+                {
+                    if (piece_length < 4 && (c >= '0' && c <= '9'))
+                    {
+                        piece_length++;
+                        year = year*10 + static_cast<std::size_t>(c - '0');
+                    }
+                    else if (c == '-' && piece_length == 4)
+                    {
+                        state = state_t::month;
+                        piece_length = 0;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::month:
+                {
+                    if (piece_length < 2 && (c >= '0' && c <= '9'))
+                    {
+                        piece_length++;
+                        month = month*10 + static_cast<std::size_t>(c - '0');
+                    }
+                    else if (c == '-' && piece_length == 2 && (month >=1 && month <= 12))
+                    {
+                        state = state_t::mday;
+                        piece_length = 0;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::mday:
+                {
+                    if (piece_length < 2 && (c >= '0' && c <= '9'))
+                    {
+                        piece_length++;
+                        mday = mday *10 + static_cast<std::size_t>(c - '0');
+                    }
+                    else if ((c == 'T' || c == 't') && piece_length == 2 && (mday <= days_in_month(year, month)))
+                    {
+                        piece_length = 0;
+                        state = state_t::hour;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::hour:
+                {
+                    if (piece_length < 2 && (c >= '0' && c <= '9'))
+                    {
+                        piece_length++;
+                        value = value*10 + static_cast<std::size_t>(c - '0');
+                    }
+                    else if (c == ':' && piece_length == 2 && (/*value >=0 && */ value <= 23))
+                    {
+                        state = state_t::minute;
+                        value = 0;
+                        piece_length = 0;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::minute:
+                {
+                    if (piece_length < 2 && (c >= '0' && c <= '9'))
+                    {
+                        piece_length++;
+                        value = value*10 + static_cast<std::size_t>(c - '0');
+                    }
+                    else if (c == ':' && piece_length == 2 && (/*value >=0 && */value <= 59))
+                    {
+                        state = state_t::second;
+                        value = 0;
+                        piece_length = 0;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::second:
+                {
+                    if (piece_length < 2 && (c >= '0' && c <= '9'))
+                    {
+                        piece_length++;
+                        value = value*10 + static_cast<std::size_t>(c - '0');
+                    }
+                    else if (piece_length == 2 && (/*value >=0 && */value <= 60)) // 00-58, 00-59, 00-60 based on leap second rules
+                    {
+                        switch (c)
+                        {
+                            case '.':
+                                value = 0;
+                                state = state_t::secfrac;
+                                break;
+                            case '+':
+                            case '-':
+                                value = 0;
+                                piece_length = 0;
+                                state = state_t::offset_hour;
+                                break;
+                            case 'Z':
+                            case 'z':
+                                state = state_t::z;
+                                break;
+                            default:
+                                return false;
+                        }
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::secfrac:
+                {
+                    if (c >= '0' && c <= '9')
+                    {
+                        value = value*10 + static_cast<std::size_t>(c - '0');
+                    }
+                    else
+                    {
+                        switch (c)
+                        {
+                            case '+':
+                            case '-':
+                                value = 0;
+                                piece_length = 0;
+                                state = state_t::offset_hour;
+                                break;
+                            case 'Z':
+                            case 'z':
+                                state = state_t::z;
+                                break;
+                            default:
+                                return false;
+                        }
+                    }
+                    break;
+                }
+                case state_t::offset_hour:
+                {
+                    if (piece_length < 2 && (c >= '0' && c <= '9'))
+                    {
+                        piece_length++;
+                        value = value*10 + static_cast<std::size_t>(c - '0');
+                    }
+                    else if (c == ':' && piece_length == 2 && (/*value >=0 && */value <= 23))
+                    {
+                        value = 0;
+                        piece_length = 0;
+                        state = state_t::offset_minute;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::offset_minute:
+                {
+                    if (piece_length < 2 && (c >= '0' && c <= '9'))
+                    {
+                        piece_length++;
+                        value = value*10 + static_cast<std::size_t>(c - '0');
+                    }
+                    else if (c == ':' && piece_length == 2 && (/*value >=0 && */value <= 59))
+                    {
+                        value = 0;
+                        piece_length = 0;
+                    }
+                    else
+                    {
+                        return false;
+                    }
+                    break;
+                }
+                case state_t::z:
+                    return false;
+            }
+        }
+
+        if (type == date_time_type::date)
+        {
+            return state == state_t::mday && piece_length == 2 && (mday >= 1 && mday <= days_in_month(year, month));
+        }
+        else
+        {
+            return state == state_t::offset_minute || state == state_t::z || state == state_t::secfrac;
+        }
+    }
+
+    // format checkers
+    using format_checker = std::function<void(const std::string& absolute_keyword_location,
+                                              const jsonpointer::json_pointer& instance_location, 
+                                              const std::string&, 
+                                              error_reporter& reporter)>;
+
+    inline
+    void rfc3339_date_check(const std::string& absolute_keyword_location,
+                            const jsonpointer::json_pointer& instance_location, 
+                            const std::string& value,
+                            error_reporter& reporter)
+    {
+        if (!validate_date_time_rfc3339(value,date_time_type::date))
+        {
+            reporter.error(validation_output("date", 
+                                             absolute_keyword_location, 
+                                             instance_location.to_uri_fragment(), 
+                                             "\"" + value + "\" is not a RFC 3339 date string"));
+        }
+    }
+
+    inline
+    void rfc3339_time_check(const std::string& absolute_keyword_location,
+                            const jsonpointer::json_pointer& instance_location, 
+                            const std::string &value,
+                            error_reporter& reporter)
+    {
+        if (!validate_date_time_rfc3339(value, date_time_type::time))        
+        {
+            reporter.error(validation_output("time", 
+                                             absolute_keyword_location, 
+                                             instance_location.to_uri_fragment(), 
+                                             "\"" + value + "\" is not a RFC 3339 time string"));
+        }
+    }
+
+    inline
+    void rfc3339_date_time_check(const std::string& absolute_keyword_location,
+                                 const jsonpointer::json_pointer& instance_location, 
+                                 const std::string &value,
+                                 error_reporter& reporter)
+    {
+        if (!validate_date_time_rfc3339(value, date_time_type::date_time))        
+        {
+            reporter.error(validation_output("date-time",  
+                                             absolute_keyword_location,
+                                             instance_location.to_uri_fragment(), 
+                                             "\"" + value + "\" is not a RFC 3339 date-time string"));
+        }
+    }
+
+    inline
+    void email_check(const std::string& absolute_keyword_location,
+                     const jsonpointer::json_pointer& instance_location, 
+                     const std::string& value,
+                     error_reporter& reporter) 
+    {
+        if (!validate_email_rfc5322(value))        
+        {
+            reporter.error(validation_output("email", 
+                                             absolute_keyword_location, 
+                                             instance_location.to_uri_fragment(), 
+                                             "\"" + value + "\" is not a valid email address as defined by RFC 5322"));
+        }
+    } 
+
+    inline
+    void hostname_check(const std::string& absolute_keyword_location,
+                        const jsonpointer::json_pointer& instance_location, 
+                        const std::string& value,
+                        error_reporter& reporter) 
+    {
+        if (!validate_hostname_rfc1034(value))
+        {
+            reporter.error(validation_output("hostname", 
+                                             absolute_keyword_location, 
+                                             instance_location.to_uri_fragment(), 
+                                             "\"" + value + "\" is not a valid hostname as defined by RFC 3986 Appendix A"));
+        }
+    } 
+
+    inline
+    void ipv4_check(const std::string& absolute_keyword_location,
+                    const jsonpointer::json_pointer& instance_location, 
+                    const std::string& value,
+                    error_reporter& reporter) 
+    {
+        if (!validate_ipv4_rfc2673(value))
+        {
+            reporter.error(validation_output("ipv4", 
+                                             absolute_keyword_location, 
+                                             instance_location.to_uri_fragment(), 
+                                             "\"" + value + "\" is not a valid IPv4 address as defined by RFC 2673"));
+        }
+    } 
+
+    inline
+    void ipv6_check(const std::string& absolute_keyword_location,
+                    const jsonpointer::json_pointer& instance_location, 
+                    const std::string& value,
+                    error_reporter& reporter) 
+    {
+        if (!validate_ipv6_rfc2373(value))
+        {
+            reporter.error(validation_output("ipv6", 
+                                             absolute_keyword_location, 
+                                             instance_location.to_uri_fragment(), 
+                                             "\"" + value + "\" is not a valid IPv6 address as defined by RFC 2373"));
+        }
+    } 
+
+    inline
+    void regex_check(const std::string& absolute_keyword_location,
+                     const jsonpointer::json_pointer& instance_location, 
+                     const std::string& value,
+                     error_reporter& reporter) 
+    {
+#if defined(JSONCONS_HAS_STD_REGEX)
+        try 
+        {
+            std::regex re(value, std::regex::ECMAScript);
+        } 
+        catch (const std::exception& e) 
+        {
+            reporter.error(validation_output("pattern", 
+                                             absolute_keyword_location, 
+                                             instance_location.to_uri_fragment(), 
+                                             "\"" + value + "\" is not a valid ECMAScript regular expression. " + e.what()));
+        }
+#endif
+    } 
+
+} // namespace jsonschema
+} // namespace jsoncons
+
+#endif // JSONCONS_JSONSCHEMA_FORMAT_CHECKERS_HPP