    """A string of characters. Each character in the string
       is a [[32-bit Unicode character|Character]]. The
       internal UTF-16 encoding is hidden from clients.

       Literal strings may be written between double quotes:

           "hello world"
           "\r\n"
           "\{#03C0} \{#2248} 3.14159"
           "\{GREEK SMALL LETTER PI} \{ALMOST EQUAL TO} 3.14159"

       Alternatively, a _verbatim string_ may be written
       between tripled double quotes.

       The _empty string_, `""`, is a string with no
       characters.

       A string is a [[Category]] of its [[characters]], and
       of its substrings:

           'w' in greeting
           "hello" in greeting

       Strings are [[summable|Summable]]:

           String greeting = "hello" + " " + "world";

       They are efficiently [[iterable|Iterable]]:

           for (char in "hello world") { ... }

       They are [[lists|List]] of [[characters|Character]]:

           value char = "hello world"[5];

       They are [[ranged|Ranged]]:

           String who = "hello world"[6...];

       Note that since `string[index]` evaluates to the
       optional type `Character?`, it is often more
       convenient to write `string[index..index]`, which
       evaluates to a `String` containing a single character,
       or to the empty string `""` if `index` refers to a
       position outside the string.

       It is easy to use comprehensions to transform strings:

           String { for (s in "hello world") if (s.letter) s.uppercased }

       Since a `String` has an underlying UTF-16 encoding,
       certain operations are expensive, requiring iteration
       of the characters of the string. In particular,
       [[size]] requires iteration of the whole string, and
       `get()`, `span()`, and `measure()` require iteration
       from the beginning of the string to the given index."""
    by ("Gavin")
    tagged("Basic types", "Strings")
    shared native final class String
            extends Object
            satisfies SearchableList<Character> &
                      Comparable<String> &
                      Summable<String> &
                      Ranged<Integer,Character,String> {

        "The concatenation of the given [[strings]]."
        see (`class StringBuilder`)
        shared static String sum({String*} strings) {
            value result = StringBuilder();
            result.appendAll(strings);
            return result.string;
        }

        "The characters that form this string."
        {Character*} characters;

        "A new string with the given [[characters]]."
        shared native new ({Character*} characters)
                extends Object() {
            this.characters = characters;
        }

        "This string, with all characters in lowercase.

         Conversion of uppercase characters to lowercase is
         performed according to a locale-independent mapping
         that produces incorrect results in certain locales
         (e.g. `tr-TR`).

         The resulting string may not have the same number
         of characters as this string, since the uppercase
         representation of certain characters comprises
         multiple characters, for example the lowercase
         representation of
         \{LATIN CAPITAL LETTER I WITH DOT ABOVE} is two
         characters wide."
        shared native String lowercased;

        "This string, with all characters in uppercase.

         Conversion of lowercase characters to uppercase is
         performed according to a locale-independent mapping
         that produces incorrect results in certain locales
         (e.g. `tr-TR`).

         The resulting string may not have the same number
         of characters as this string, since the uppercase
         representation of certain characters comprises
         multiple characters, for example the uppercase
         representation of \{LATIN SMALL LETTER SHARP S} is
         SS."
        shared native String uppercased;

        "Split the string into tokens, using the given
         [[predicate function|splitting]] to determine which
         characters are _separator characters_ delimiting
         token boundaries.

             value pathElements = path.split('/'.equals);

         The flags [[discardSeparators]] and [[groupSeparators]]
         determine how separator characters occur in the
         resulting stream.

         - If `discardSeparators` is enabled, the stream
           contains only _regular tokens_ containing
           adjacent non-separator characters, and the
           separator characters are simply discarded.
         - If `discardSeparators` is disabled, the string is
           broken into regular tokens and _separator tokens_
           containing the separator characters. If
           `groupSeparators` is disabled, the separator
           tokens each contain a single character. If
           `groupSeparators` is enabled, adjacent separator
           characters are grouped into a single token.

         The [[limit]] determines the maximum number of
         regular (non-separator) tokens that are returned in
         the stream. If the limit is exceeded, the remainder
         of the string is returned as a single token at the
         end of the resulting stream. For example,

             \"foo bar baz fum\".split { limit = 2; }

         produces the stream `{ \"foo\", \"bar\", \"baz fum\" }`.

         If the first character of this string is a
         separator character, the stream begins with an
         empty token. Likewise, if the last character of
         this string is a separator character, and the
         `limit` is not reached, the stream ends with an
         empty token.

         Note that for the case of the empty string, `split()`
         always produces a stream containing a single empty
         token. For example:

             \"\".split('/'.equals)

         evaluates to the nonempty stream `{ \"\" }`."
        shared native {String+} split(
                "A predicate that determines if a character
                 is a separator characters at which to split.
                 Default to split at any
                 [[whitespace|Character.whitespace]]
                 character."
                Boolean splitting(Character ch) => ch.whitespace,
                "Specifies that separator characters
                 occurring in the string should be discarded.
                 If `false`, the resulting stream will have
                 separator tokens containing the separator
                 characters."
                Boolean discardSeparators = true,
                "Specifies that adjacent separator
                 characters should be grouped into a single
                 separator token. If `false` each separator
                 token will contain a single character."
                Boolean groupSeparators = true,
                "Specifies the maximum number of regular
                 tokens, with a `null` argument indicating
                 no upper limit. If this string contains
                 more regular tokens than the given limit,
                 the remaining part of the string will be
                 returned as a single token at the very end
                 of the stream. If the limit is not strictly
                 positive, a stream containing this string
                 will be returned."
                since("1.3.2")
                Integer? limit = null)
                => StringTokens(this, splitting,
                    discardSeparators, groupSeparators,
                    limit);

        "The first character in the string."
        shared actual native Character? first;

        "The last character in the string."
        shared actual native Character? last;

        "The rest of the string, without its first character."
        shared actual native String rest;

        "A sequence containing all indexes of this string."
        shared actual native Integer[] keys => 0:size;

        "Join the [[string representations|Object.string]]
         of the given [[objects]], using this string as a
         separator."
        shared native String join({Object*} objects) {
            value result = StringBuilder();
            value strings = objects.map(Object.string);
            result.appendAll(empty then strings
                else strings.interpose(this));
            return result.string;
        }

        "Split the string into lines of text, discarding
         line breaks. Recognized line break sequences are
         `\\n` and `\\r\\n`. The empty string is considered
         a single line of text."
        see (`value linesWithBreaks`)
        shared native {String+} lines
                => split('\n'.equals, true, false)
                   .spread(String.trimTrailing)('\r'.equals);

        "Split the string into lines of text with line
         breaks. Each line will be terminated by a line
         break sequence, `\\n` or `\\r\\n`, except for the
         very last line. The empty string is considered a
         single line of text."
        see (`value lines`)
        since("1.1.0")
        shared native {String+} linesWithBreaks
                => split('\n'.equals, false, false)
                .partition(2)
                .map(([line, *rest])
                        => if (nonempty rest)
                        then line + rest[0]
                        else line);

        "A string containing the characters of this string,
         after discarding [[whitespace|Character.whitespace]]
         from the beginning and end of the string."
        shared native String trimmed
                => trim(Character.whitespace);

        "A string containing the characters of this string,
         after discarding the characters matching the given
         [[predicate function|trimming]] from the beginning
         and end of the string.

             value trimmed = name.trim('_'.equals);

         A character is removed from the string if it
         matches the given predicate and if either:

         - every character occurring earlier in the string
           also matches the predicate, or
         - every character occurring later in the string
           also matches the predicate."
        shared actual native String trim(
                "A predicate that determines whether a
                 character occurring near the start or end
                 of the string should be trimmed."
                Boolean trimming(Character element))
                => if (exists from
                        = firstIndexWhere(not(trimming)),
                       exists to
                        = lastIndexWhere(not(trimming)))
                then this[from..to]
                else "";

        "A string containing the characters of this string,
         after discarding the characters matching the given
         [[predicate function|trimming]] from the beginning
         of the string.

         A character is removed from the string if it
         matches the given predicate and every character
         occurring earlier in the string also matches the
         predicate."
        shared actual native String trimLeading(
                "A predicate that determines whether a
                 character occurring near the start of the
                 string should be trimmed."
                Boolean trimming(Character element))
                => if (exists from
                        = firstIndexWhere(not(trimming)))
                then this[from...]
                else "";

        "A string containing the characters of this string,
         after discarding the characters matching the given
         [[predicate function|trimming]] from the end of the
         string.

         A character is removed from the string if it
         matches the given predicate and every character
         occurring later in the string also matches the
         predicate."
        shared actual native String trimTrailing(
                "The predicate that determines whether a
                 character occurring near the end of the
                 string should be trimmed."
                Boolean trimming(Character element))
                => if (exists to
                        = lastIndexWhere(not(trimming)))
                then this[...to]
                else "";

        "A string containing the characters of this string
         after collapsing strings of adjacent
         [[whitespace|Character.whitespace]] characters into
         single space characters and discarding whitespace
         from the beginning and end of the string."
        shared native String normalized {
            value result = StringBuilder();
            variable value previousWasWs = false;
            for (ch in this) {
                value currentIsWs = ch.whitespace;
                if (!currentIsWs) {
                    result.appendCharacter(ch);
                }
                else if (!previousWasWs) {
                    result.appendCharacter(' ');
                }
                previousWasWs = currentIsWs;
            }
            return result.string.trimmed;
        }

        "A string containing the characters of this string,
         with the characters in reverse order."
        shared native actual String reversed
                => StringBuilder()
                    .append(this)
                    .reverseInPlace()
                    .string;

        "Determine if this string contains only
         [[whitespace characters|Character.whitespace]].
         Returns `false` if the string contains at least one
         character which is not a whitespace character."
        shared native Boolean whitespace
                => every(Character.whitespace);

        "Determines if this string contains a character at
         the given [[index]], that is, if `0<=index<size`."
        shared native actual Boolean defines(Integer index)
                => 0<=index<size;

        "A string containing the characters of this string
         occurring between the given indexes. If the
         [[start index|from]] is the same as the
         [[end index|to]], return a string with a single
         character. If the start index is larger than the
         end index, return the characters in the reverse
         order from the order in which they occur in this
         string. If both the start index and the end index
         are larger than the last index in the string, or if
         both the start index and the end index are smaller
         than the first index in the string, return the
         empty string. Otherwise, if the last index is
         larger than the last index in the string, return
         all characters from the start index to last
         character of the string.

         Using the [[span operator|Ranged.span]],
         `string.span(to, from)` may be written as
         `string[from..to]`."
        shared actual native String span(Integer from,
                                         Integer to);

        "A string containing the characters of this string
         from the given [[start index|from]] inclusive to
         the end of the string. If the start index is larger
         than the last index of the string, return the empty
         string. If the start index is negative, return this
         string.

         Using the [[span operator|Ranged.spanFrom]],
         `string.spanFrom(from)` may be written as
         `string[from...]`."
        shared actual native String spanFrom(Integer from)
                => from<size then span(from, size) else "";

        "A string containing the characters of this string
         from the start of the string up to and including
         the given [[end index|to]]. If the end index is
         negative, return the empty string. If the end index
         is larger than the last index in this string,
         return this string.

         Using the [[span operator|Ranged.spanTo]],
         `string.spanTo(to)` may be written as
         `string[...to]`."
        shared actual native String spanTo(Integer to)
                => to>=0 then span(0, to) else "";

        "A string containing the characters of this string
         beginning at the given [[start index|from]],
         returning a string no longer than the given
         [[length]]. If the portion of this string starting
         at the given index is shorter than the given length,
         return the portion of this string from the given
         index until the end of this string. Otherwise,
         return a string of the given length. If the start
         index is larger than the last index of the string,
         return the empty string.

         Using the [[measure operator|Ranged.measure]],
         `string.measure(from, length)` may be written as
         `string[from:length]`."
        shared native actual String measure(Integer from,
                                            Integer length);

        "Select the first characters of this string,
         returning a string no longer than the given
         [[length]]. If this string is shorter than the
         given length, return this string. Otherwise, return
         a string of the given length."
        shared native actual String initial(Integer length)
                => this[0:length];

        "Select the last characters of the string, returning
         a string no longer than the given [[length]]. If
         this string is shorter than the given length,
         return this string. Otherwise, return a string of
         the given length."
        shared native actual String terminal(Integer length)
                => this[size-length:length];

        "Return two strings, the first containing the
         characters that occur before the given [[index]],
         the second with the characters that occur after the
         given `index`. If the given `index` is outside the
         range of indices of this string, one of the
         returned strings will be empty."
        shared native actual String[2] slice(Integer index)
                => [this[...index-1], this[index...]];

        "The length of the string (the number of characters
         it contains). In the case of the empty string, the
         string has length zero. Note that this operation is
         potentially costly for long strings, since the
         underlying representation of the characters uses a
         UTF-16 encoding. Use of [[longerThan]] or
         [[shorterThan]] is highly recommended."
        see (`function longerThan`, `function shorterThan`)
        aliased ("length")
        shared actual native Integer size;

        "The index of the last character in the string, or
         `null` if the string has no characters. Note that
         this operation is potentially costly for long
         strings, since the underlying representation of the
         characters uses a UTF-16 encoding. For any nonempty
         string:

             string.lastIndex == string.size-1"
        shared actual Integer? lastIndex
                => if (size==0) then null else size-1;

        "An iterator for the characters of the string."
        shared actual native Iterator<Character> iterator();

        "Returns the character at the given [[index]] in the
         string, or `null` if the index is before the start
         of the string or past the end of string. The first
         character in the string occurs at index zero. The
         last character in the string occurs at index
         `string.size-1`.

         Using the [[item operator|Correspondence.get]],
         `string.getFromFirst(index)` may be written as
         `string[index]`."
        see (`function getFromLast`)
        shared actual native Character? getFromFirst(
            "An index from the start of the string, which
             identifies a character within the string only
             if it falls within the range `0:size`. The
             index `0` refers to the first character in the
             string."
            Integer index);

        "Get the character at the specified index, where the
         string is indexed from the _end_ of the string, or
         `null` if the index falls outside the bounds of
         this string."
        see (`function getFromFirst`)
        shared actual native Character? getFromLast(
            "An index from the end of the string, which
             identifies a character within this string only
             if it falls within the range `0:size`. The
             index `0` refers to the last character in the
             string."
            Integer index);

        "Determines if the given object is a `String` and,
         if so, if it occurs as a substring of this string,
         or if the object is a `Character` that occurs in
         this string. That is to say, a string is considered
         a [[Category]] of its substrings and of its
         characters.

         Using the [[`in` operator|Category.contains]],
         `string.contains(element)` may be written as
         `element in string`."
        shared actual native Boolean contains(Object element)
                => switch (element)
                case (is String) includes(element)
                case (is Character) occurs(element)
                else false;

        "Determines if this string starts with the
         characters of the given string or list. Returns
         `false` if the given list contains an element that
         is not a [[Character]]."
        shared actual native Boolean startsWith(
            "A sequence of [[Character]]s, usually a
             `String`."
            List<> substring)
                => if (is String substring)
                then includesAt(0, substring)
                else super.startsWith(substring);

        "Determines if this string ends with the characters
         of the given string or list. Returns `false` if the
         given list contains an element that is not a
         [[Character]]."
        shared actual native Boolean endsWith(
            "A sequence of [[Character]]s, usually a
             `String`."
            List<> substring)
                => if (is String substring)
                then includesAt(size-substring.size, substring)
                else super.endsWith(substring);

        "Returns the concatenation of this string with the
         given string. The resulting string contains the
         characters of this string followed by the
         characters of the given string.

         Using the [[addition operator|Summable.plus]],
         `string.plus(otherString)` may be written as
         `string + otherString`."
        shared actual native String plus(String other);

        "Returns a string formed by repeating this string
         the given number of [[times]], or the empty string
         if `times<=0`."
        shared actual native String repeat(Integer times) {
            value result = StringBuilder();
            for (_ in 0:times) {
                result.append(this);
            }
            return result.string;
        }

        "Returns a string formed by replacing every
         occurrence in this string of the given nonempty
         [[substring]] with the given [[replacement]] string,
         working from the start of this string to the end."
        throws (`class AssertionError`,
                "if the given [[substring]] is empty")
        shared native String replace(String substring,
                                     String replacement) {
            "string to replace must be nonempty"
            assert (!substring.empty);
            value firstIndex = firstInclusion(substring);
            if (!exists firstIndex) {
                return this;
            }
            value substringLength = substring.size;
            value replacementLength = replacement.size;
            value result = StringBuilder().append(this);
            variable value index = firstIndex;
            while (true) {
                result.replace {
                    index = index;
                    length = substringLength;
                    string = replacement;
                };
                if (exists nextIndex
                    = result.firstInclusion(substring,
                            index + replacementLength)) {
                    index = nextIndex;
                }
                else {
                    break;
                }
            }
            return result.string;
        }

        "Returns a string formed by replacing the first
         occurrence in this string of the given nonempty
         [[substring]], if any, with the given
         [[replacement]] string."
        throws (`class AssertionError`,
                "if the given [[substring]] is empty")
        since("1.1.0")
        shared native String replaceFirst(String substring,
                                          String replacement) {
            "string to replace must be nonempty"
            assert (!substring.empty);
            return
                if (exists index = firstInclusion(substring))
                then initial(index)
                        + replacement
                        + spanFrom(index+substring.size)
                else this;
        }

        "Returns a string formed by replacing the last
         occurrence in this string of the given nonempty
         [[substring]], if any, with the given
         [[replacement]] string."
        throws (`class AssertionError`,
                "if the given [[substring]] is empty")
        since("1.1.0")
        shared native String replaceLast(String substring,
                                         String replacement) {
            "string to replace must be nonempty"
            assert (!substring.empty);
            return
                if (exists index = lastInclusion(substring))
                then initial(index)
                        + replacement
                        + spanFrom(index+substring.size)
                else this;
        }

        "Returns a string formed by removing the given
         [[prefix]] from the start of this string, if this
         string [[starts with|startsWith]] the given `prefix`,
         or this string otherwise."
        since("1.3.0")
        shared native String removeInitial(String prefix)
                => startsWith(prefix)
                then spanFrom(prefix.size)
                else this;

        "Returns a string formed by removing the given
         [[postfix]] from the end of this string, if this
         string [[ends with|endsWith]] the given `postfix`,
         or this string otherwise."
        since("1.3.0")
        shared native String removeTerminal(String postfix)
                => endsWith(postfix)
                then spanTo(size-postfix.size)
                else this;

        function charsEqualIgnoringCase(Character x, Character y)
                => x==y
                || x.uppercased==y.uppercased
                || x.lowercased==y.lowercased;

        "Compare this string with the given string
         lexicographically, according to the Unicode code
         points of the characters.

         This defines a locale-independent collation that is
         incorrect in some locales.

         For more specialized lexicographic comparisons
         between strings, use [[compareIgnoringCase]] or
         [[compareCorresponding]]."
        see (`function compareIgnoringCase`,
             `function compareCorresponding`)
        shared actual native Comparison compare(String other)
                => compareCorresponding(this, other,
                    (Character x, Character y) => x<=>y);

        "Compare this string with the given string
         lexicographically, ignoring the case of the
         characters. That is, by considering two characters
         `x` and `y` as equal if:

         - `x == y`,
         - `x.uppercased == y.uppercased`, or
         - `x.lowercased == y.lowercased`.

         This defines a locale-independent collation that is
         incorrect in some locales.

         For more specialized lexicographic comparisons
         between strings, use [[compareCorresponding]]."
        see (`value Character.lowercased`,
             `value Character.uppercased`,
             `function compareCorresponding`)
        since("1.2.0")
        shared native Comparison compareIgnoringCase(String other)
                => compareCorresponding(this, other,
                    (Character x, Character y)
                            => charsEqualIgnoringCase(x, y)
                            then equal
                            else x.lowercased <=> y.lowercased);

        "Determines if this string is longer than the given
         [[length]]. This is a more efficient operation than
         `string.size>length`."
        see (`value size`)
        shared actual native Boolean longerThan(Integer length);

        "Determines if this string is shorter than the given
         [[length]]. This is a more efficient operation than
         `string.size>length`."
        see (`value size`)
        shared actual native Boolean shorterThan(Integer length);

        "Determines if the given object is a `String`, and
         if so, if this string has the same [[length|size]],
         and the same [[characters]], in the same order, as
         the given [[string|that]].

         For more specialized character-wise comparisons
         between strings, use [[equalsIgnoringCase]] or
         [[corresponding]]."
        see (`function equalsIgnoringCase`,
             `function corresponding`)
        shared actual native Boolean equals(Object that)
                => if (is String that)
                then corresponding(this, that,
                        (Character x, Character y) => x==y)
                else false;

        "Compare this string with the given string, ignoring
         the case of the characters. That is, by considering
         two characters `x` and `y` as equal if:

         - `x == y`,
         - `x.uppercased == y.uppercased`, or
         - `x.lowercased == y.lowercased`.

         For more specialized character-wise comparisons
         between strings, use [[corresponding]]."
        see (`value Character.lowercased`,
             `value Character.uppercased`,
             `function corresponding`)
        since("1.2.0")
        shared native Boolean equalsIgnoringCase(String that)
                => corresponding(this, that,
                    charsEqualIgnoringCase);

        "A hash code for this `String`, computed from its
         UTF-16 code units."
        shared actual native Integer hash;

        "This string."
        shared actual String string => this;

        "Determines if this string has no characters, that
         is, if it has zero [[size]]. This is a _much_ more
         efficient operation than `string.size==0`."
        see (`value size`)
        shared actual native Boolean empty;

        "This string."
        shared actual String coalesced => this;

        "This string."
        shared actual String clone() => this;

        "Pad this string with the given [[character]],
         producing a string of the given minimum [[size]],
         centering the string. If this string is not smaller
         than the given `size`, return this string."
        since("1.1.0")
        shared native String pad(Integer size,
            "The padding character."
            Character character=' ') {
            value length = this.size;
            if (size<=length) {
                return this;
            }
            value left = (size-length)/2;
            value right = left + (size-length)%2;
            value builder = StringBuilder();
            for (_ in 0:left) {
                builder.appendCharacter(character);
            }
            builder.append(this);
            for (_ in 0:right) {
                builder.appendCharacter(character);
            }
            return builder.string;
        }

        "Left pad this string with the given [[character]],
         producing a string of the given minimum [[size]].
         If this string is not smaller than the given `size`,
         return this string."
        since("1.1.0")
        shared native String padLeading(Integer size,
            "The padding character."
            Character character=' ') {
            value length = this.size;
            if (size<=length) {
                return this;
            }
            value builder = StringBuilder();
            for (_ in 0:size-length) {
                builder.appendCharacter(character);
            }
            builder.append(this);
            return builder.string;
        }

        "Right pad this string with the given [[character]],
         producing a string of the given minimum [[size]].
         If this string is not smaller than the given `size`,
         return this string."
        since("1.1.0")
        shared native String padTrailing(Integer size,
            "The padding character."
            Character character=' ') {
            value length = this.size;
            if (size<=length) {
                return this;
            }
            value builder = StringBuilder();
            builder.append(this);
            for (_ in 0:size-length) {
                builder.appendCharacter(character);
            }
            return builder.string;
        }

        "Efficiently copy the characters in the segment
         `sourcePosition:length` of this string to the
         segment `destinationPosition:length` of the given
         [[character array|destination]].

         The given [[sourcePosition]] and [[destinationPosition]]
         must be non-negative and, together with the given
         [[length]], must identify meaningful ranges within
         the two lists, satisfying:

         - `size >= sourcePosition+length`, and
         - `destination.size >= destinationPosition+length`.

         If the given `length` is not strictly positive, no
         elements are copied."
        throws (`class AssertionError`,
            "if the arguments do not identify meaningful
             ranges within the two lists:

             - if the given [[sourcePosition]] or
               [[destinationPosition]] is negative,
             - if `size < sourcePosition+length`, or
             - if `destination.size < destinationPosition+length`.")
        since("1.2.0")
        shared native
        void copyTo(
            "The array into which to copy the elements."
            Array<in Character> destination,
            "The index of the first element in this array to
             copy."
            Integer sourcePosition = 0,
            "The index in the given array into which to copy
             the first element."
            Integer destinationPosition = 0,
            "The number of elements to copy."
            Integer length
                    = smallest(size - sourcePosition,
                        destination.size - destinationPosition));

        "A string containing the characters of this string
         beginning at the given [[start index|from]], up to,
         but not including, the given [[end index|end]]. If
         the given end index is greater than the last index
         of this string, return the portion of the string
         from the given start index until the end of the
         string. If the start index is larger than the last
         index of the string, or if the end index is less
         than one or less than the start index, return the
         empty string.

         For every pair of indexes, `start`, and `end`, and
         for any `string`:

             string.substring(start, end) == string[start:end-start]

         _Note: this operation is provided to ease migration
         of code written in other languages. It is more
         idiomatic to use [[measure]] or [[span]] where
         reasonable._"
        see (`function measure`, `function span`)
        since("1.3.0")
        shared native String substring(
            "The inclusive start index."
            Integer from = 0,
            "The exclusive end index."
            Integer end = size)
                => this[from:end-from];

        "The first index greater than or equal to the given
         [[start index|from]] at which the given substring
         occurs in this string, if any, or `-1` otherwise.

         For any `string` and `substring`, and for every
         index `from`:

             string.indexOf(substring, from)
                == string.firstInclusion(substring, from)
                        else -1

         _Note: this operation is provided to ease migration
         of code written in other languages. It is more
         idiomatic to use [[firstInclusion]] where
         reasonable._"
        see (`function firstInclusion`)
        since("1.3.0")
        shared native Integer indexOf(
            "The substring to find within this string."
            String string,
            "The inclusive start index."
            Integer from = 0)
                => firstInclusion(string, from) else -1;

        "The last index smaller than or equal to the given
         [[end index|to]] at which the given substring
         occurs in this string, if any, or `-1` otherwise.

         For any `string` and `substring`, and for every
         index `from`:

             string.lastIndexOf(substring, from)
                == string.lastInclusion(substring, string.size-from)
                        else -1

         _Note: this operation is provided to ease migration
         of code written in other languages. It is more
         idiomatic to use [[lastInclusion]] where
         reasonable._"
        see (`function lastInclusion`)
        since("1.3.0")
        shared native Integer lastIndexOf(
            "The substring to find within this string."
            String string,
            "The inclusive start index."
            Integer to = size)
                => lastInclusion(string, size-to) else -1;

        "Determines if this string occurs after the given
         string in lexicographic order, returning `false` if
         the two strings are equal."
        shared actual native Boolean largerThan(String other)
                => super.largerThan(other);

        "Determines if this string occurs before the given
         string in lexicographic order, returning `false` if
         the two strings are equal."
        shared actual native Boolean smallerThan(String other)
                => super.smallerThan(other);

        "Determines if this string occurs after the given
         string in lexicographic order, returning `true` if
         the two strings are equal."
        shared actual native Boolean notSmallerThan(String other)
                => super.notSmallerThan(other);

        "Determines if this string occurs before the given
         string in lexicographic order, returning `true` if
         the two strings are equal."
        shared actual native Boolean notLargerThan(String other)
                => super.notLargerThan(other);

        shared actual native List<Character> sublistFrom(Integer from);
        shared actual native List<Character> sublistTo(Integer to);

        shared actual native {Integer*} indexesWhere(Boolean selecting(Character element));
        shared actual native Integer? firstIndexWhere(Boolean selecting(Character element));
        shared actual native Integer? lastIndexWhere(Boolean selecting(Character element));

        shared actual native {Integer*} occurrences(Character element, Integer from, Integer length);
        shared actual native {Integer*} inclusions(List<Character> sublist, Integer from);

        shared actual native Boolean occurs(Character element, Integer from, Integer length);
        shared actual native Boolean occursAt(Integer index, Character element);
        shared actual native Boolean includes(List<Character> sublist, Integer from);
        shared actual native Boolean includesAt(Integer index, List<Character> sublist);

        shared actual native Integer? firstOccurrence(Character element, Integer from, Integer length);
        shared actual native Integer? lastOccurrence(Character element, Integer from, Integer length);
        shared actual native Integer? firstInclusion(List<Character> sublist, Integer from);
        shared actual native Integer? lastInclusion(List<Character> sublist, Integer from);

        shared actual native void each(void step(Character element));
        shared actual native Integer count(Boolean selecting(Character element));
        shared actual native Boolean every(Boolean selecting(Character element));
        shared actual native Boolean any(Boolean selecting(Character element));
        shared actual native Result|Character|Null reduce<Result>
                (Result accumulating(Result|Character partial, Character element));
        shared actual native Character? find(Boolean selecting(Character element));
        shared actual native Character? findLast(Boolean selecting(Character element));
        shared actual native <Integer->Character>? locate(Boolean selecting(Character element));
        shared actual native <Integer->Character>? locateLast(Boolean selecting(Character element));
        shared actual native {<Integer->Character>*} locations(Boolean selecting(Character element));
    }