[section Concepts]

[h2 CharT requirements]
If type `BidiIterT` is used as a template argument to _basic_regex_, then `CharT` is
`iterator_traits<BidiIterT>::value_type`. Type `CharT` must have a trivial default
constructor, copy constructor, assignment operator, and destructor.  In addition
the following requirements must be met for objects; `c` of type `CharT`, `c1` and `c2` of
type `CharT const`, and `i` of type `int`:

[table CharT Requirements
    [
        [[*Expression]]
        [[*Return type]]
        [[*Assertion / Note / Pre- / Post-condition]]
    ]
    [
        [`CharT c`]
        [`CharT`]
        [Default constructor (must be trivial).]
    ]
    [
        [`CharT c(c1)`]
        [`CharT`]
        [Copy constructor (must be trivial).]
    ]
    [
        [`c1 = c2`]
        [`CharT`]
        [Assignment operator (must be trivial).]
    ]
    [
        [`c1 == c2`]
        [`bool`]
        [`true` if `c1` has the same value as `c2`.]
    ]
    [
        [`c1 != c2`]
        [`bool`]
        [`true` if `c1` and `c2` are not equal.]
    ]
    [
        [`c1 < c2`]
        [`bool`]
        [`true` if the value of `c1` is less than `c2`.]
    ]
    [
        [`c1 > c2`]
        [`bool`]
        [`true` if the value of `c1` is greater than `c2`.]
    ]
    [
        [`c1 <= c2`]
        [`bool`]
        [`true` if `c1` is less than or equal to `c2`.]
    ]
    [
        [`c1 >= c2`]
        [`bool`]
        [`true` if `c1` is greater than or equal to `c2`.]
    ]
    [
        [`intmax_t i = c1`]
        [`int`]
        [
            `CharT` must be convertible to an integral type.
        ]
    ]
    [
        [`CharT c(i);`]
        [`CharT`]
        [`CharT` must be constructable from an integral type.]
    ]
]

[h2 Traits Requirements]
In the following table `X` denotes a traits class defining types and functions 
for the character container type `CharT`; `u` is an object of type `X`; `v` is an 
object of type `const X`; `p` is a value of type `const CharT*`; `I1` and `I2` are 
`Input Iterators`; `c` is a value of type `const CharT`; `s` is an object of type 
`X::string_type`; `cs` is an object of type `const X::string_type`; `b` is a value of 
type `bool`; `i` is a value of type `int`; `F1` and `F2` are values of type `const CharT*`; 
`loc` is an object of type `X::locale_type`; and `ch` is an object of `const char`.

[table Traits Requirements
    [
        [
            [*Expression]
        ]
        [
            [*Return type]
        ]
        [
            [*Assertion / Note\n
                Pre / Post condition]
        ]
    ]
    [
        [
            `X::char_type`
        ]
        [
            `CharT`
        ]
        [
            The character container type used in the implementation of class template _basic_regex_.
        ]
    ]
    [
        [
            `X::string_type`
        ]
        [
            `std::basic_string<CharT>` or `std::vector<CharT>`
        ]
        [
            
        ]
    ]
    [
        [
            `X::locale_type`
        ]
        [
            ['Implementation defined]
        ]
        [
            A copy constructible type that represents the locale used by the traits class.
        ]
    ]
    [
        [
            `X::char_class_type`
        ]
        [
            ['Implementation defined]
        ]
        [
            A bitmask type representing a particular character classification. Multiple 
                values of this type can be bitwise-or'ed together to obtain a new valid value.
        ]
    ]
    [
        [
            `X::hash(c)`
        ]
        [
            `unsigned char`
        ]
        [
            Yields a value between `0` and `UCHAR_MAX` inclusive.
        ]
    ]
    [
        [
            `v.widen(ch)`
        ]
        [
            `CharT`
        ]
        [
            Widens the specified `char` and returns the resulting `CharT`.
        ]
    ]
    [
        [
            `v.in_range(r1, r2, c)`
        ]
        [
            `bool`
        ]
        [
            For any characters `r1` and `r2`, returns `true` if `r1 <= c && c <= r2`.
                Requires that `r1 <= r2`.
        ]
    ]
    [
        [
            `v.in_range_nocase(r1, r2, c)`
        ]
        [
            `bool`
        ]
        [
            For characters `r1` and `r2`, returns `true` if there is some character
                `d` for which `v.translate_nocase(d) == v.translate_nocase(c)` and
                `r1 <= d && d <= r2`. Requires that `r1 <= r2`.
        ]
    ]
    [
        [
            `v.translate(c)`
        ]
        [
            `X::char_type`
        ]
        [
            Returns a character such that for any character `d` that is to be considered 
                equivalent to `c` then `v.translate(c) == v.translate(d)`.
        ]
    ]
    [
        [
            `v.translate_nocase(c)`
        ]
        [
            `X::char_type`
        ]
        [
            For all characters `C` that are to be considered 
            equivalent to `c` when comparisons are to be performed without regard to case, 
            then `v.translate_nocase(c) == v.translate_nocase(C)`.
        ]
    ]
    [
        [
            `v.transform(F1, F2)`
        ]
        [
            `X::string_type`
        ]
        [
            Returns a sort key for the character sequence designated by the iterator range 
                `[F1, F2)` such that if the character sequence `[G1, G2)` sorts before the 
                character sequence `[H1, H2)` then `v.transform(G1, G2) < v.transform(H1, H2)`. 
        ]
    ]
    [
        [
            `v.transform_primary(F1, F2)`
        ]
        [
            `X::string_type`
        ]
        [
            Returns a sort key for the character sequence designated by the iterator range 
                `[F1, F2)` such that if the character sequence `[G1, G2)` sorts before the 
                character sequence `[H1, H2)` when character case is not considered then 
                `v.transform_primary(G1, G2) < v.transform_primary(H1, H2)`.
        ]
    ]
    [
        [
            `v.lookup_classname(F1, F2)`
        ]
        [
            `X::char_class_type`
        ]
        [
            Converts the character sequence designated by the iterator range `[F1,F2)` into a 
                bitmask type that can subsequently be passed to `isctype`. Values returned from 
                `lookup_classname` can be safely bitwise or'ed together. Returns `0` if the 
                character sequence is not the name of a character class recognized by `X`. The 
                value returned shall be independent of the case of the characters in the 
                sequence.
        ]
    ]
    [
        [
            `v.lookup_collatename(F1, F2)`
        ]
        [
            `X::string_type`
        ]
        [
            Returns a sequence of characters that represents the collating element 
                consisting of the character sequence designated by the iterator range `[F1, F2)`. 
                Returns an empty string if the character sequence is not a valid collating 
                element.
        ]
    ]
    [
        [
            `v.isctype(c, v.lookup_classname(F1, F2))`
        ]
        [
            `bool`
        ]
        [
            Returns `true` if character `c` is a member of the character class designated by 
                the iterator range `[F1, F2)`, `false` otherwise.
        ]
    ]
    [
        [
            `v.value(c, i)`
        ]
        [
            `int`
        ]
        [
            Returns the value represented by the digit `c` in base `i` if the character `c` is a 
                valid digit in base `i`; otherwise returns `-1`.\n
                \[Note: the value of `i` will only be `8`, `10`, or `16`. -end note\]
        ]
    ]
    [
        [
            `u.imbue(loc)`
        ]
        [
            `X::locale_type`
        ]
        [
            Imbues `u` with the locale `loc`, returns the previous 
                locale used by `u`. 
        ]
    ]
    [
        [
            `v.getloc()`
        ]
        [
            `X::locale_type`
        ]
        [
            Returns the current locale used by `v`. 
        ]
    ]
]

[h2 Acknowledgements]

This section is adapted from the equivalent page in the _regexpp_ documentation and from the
_proposal_ to add regular expressions to the Standard Library.

[endsect]
