whereas `q` and `s` expect a
        string.

        This function does not accept string values containing embedded zeros.

string.gmatch({s}, {pattern})                                  *string.gmatch()*
        Returns an |iterator| function that, each time it is called, returns the
        next captures from {pattern} over string {s}.

        If {pattern} specifies no captures, then the whole match is produced
        in each call.

        As an example, the following loop
>lua
               s = "hello world from Lua"
               for w in string.gmatch(s, "%a+") do
                 print(w)
               end
<
        will iterate over all the words from string {s}, printing one per
        line. The next example collects all pairs `key=value` from the given
        string into a table:
>lua
               t = {}
               s = "from=world, to=Lua"
               for k, v in string.gmatch(s, "(%w+)=(%w+)") do
                 t[k] = v
               end
<

string.gsub({s}, {pattern}, {repl} [, {n}])                      *string.gsub()*
        Returns a copy of {s} in which all occurrences of the {pattern} have
        been replaced by a replacement string specified by {repl}, which may
        be a string, a table, or a function. `gsub` also returns, as its
        second value, the total number of substitutions made.

        If {repl} is a string, then its value is used for replacement. The
        character `%` works as an escape character: any sequence in {repl} of
        the form `%n`, with {n} between 1 and 9, stands for the value of the
        {n} -th captured substring (see below). The sequence `%0` stands for
        the whole match. The sequence `%%` stands for a single `%`.

        If {repl} is a table, then the table is queried for every match, using
        the first capture as the key; if the pattern specifies no captures,
        then the whole match is used as the key.

        If {repl} is a function, then this function is called every time a
        match occurs, with all captured substrings passed as arguments, in
        order; if the pattern specifies no captures, then the whole match is
        passed as a sole argument.

        If the value returned by the table query or by the function call is a
        string or a number, then it is used as the replacement string;
        otherwise, if it is `false` or `nil`, then there is no replacement
        (that is, the original match is kept in the string).

        The optional last parameter {n} limits the maximum number of
        substitutions to occur. For instance, when {n} is 1 only the first
        occurrence of `pattern` is replaced.

        Here are some examples:
>lua
           x = string.gsub("hello world", "(%w+)", "%1 %1")
           --> x="hello hello world world"

           x = string.gsub("hello world", "%w+", "%0 %0", 1)
           --> x="hello hello world"

           x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
           --> x="world hello Lua from"

           x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
           --> x="home = /home/roberto, user = roberto"

           x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
                 return loadstring(s)()
               end)
           --> x="4+5 = 9"

           local t = {name="lua", version="5.1"}
           x = string.gsub("$name%-$version.tar.gz", "%$(%w+)", t)
           --> x="lua-5.1.tar.gz"
<

string.len({s})                                                   *string.len()*
        Receives a string and returns its length. The empty string `""` has
        length 0. Embedded zeros are counted, so `"a\000b\000c"` has length 5.

string.lower({s})                                               *string.lower()*
        Receives a string and returns a copy of this string with all uppercase
        letters changed to lowercase. All other characters are left unchanged.
        The definition of what an uppercase