`^$()%.[]*+-?`)
          represents the character `x` itself.
    - `.`   (a dot) represents all characters.
    - `%a`  represents all letters.
    - `%c`  represents all control characters.
    - `%d`  represents all digits.
    - `%l`  represents all lowercase letters.
    - `%p`  represents all punctuation characters.
    - `%s`  represents all space characters.
    - `%u`  represents all uppercase letters.
    - `%w`  represents all alphanumeric characters.
    - `%x`  represents all hexadecimal digits.
    - `%z`  represents the character with representation `0`.
    - `%x`  (where `x` is any non-alphanumeric character) represents the
          character `x`. This is the standard way to escape the magic
          characters. Any punctuation character (even the non-magic) can be
          preceded by a `%` when used to represent itself in a pattern.

    - `[set]`  represents the class which is the union of all characters in
         `set`. A range of characters may be specified by separating the end
         characters of the range with a `-`. All classes `%x` described
         above may also be used as components in `set`. All other characters
         in `set` represent themselves. For example, `[%w_]` (or `[_%w]`)
         represents all alphanumeric characters plus the underscore, `[0-7]`
         represents the octal digits, and `[0-7%l%-]` represents the octal
         digits plus the lowercase letters plus the `-` character.

         The interaction between ranges and classes is not defined. Therefore,
         patterns like `[%a-z]` or `[a-%%]` have no meaning.

    - `[^set]`  represents the complement of `set`, where `set` is interpreted
         as above.

For all classes represented by single letters (`%a`, `%c`, etc.), the
corresponding uppercase letter represents the complement of the class. For
instance, `%S` represents all non-space characters.

The definitions of letter, space, and other character groups depend on the
current locale. In particular, the class `[a-z]` may not be equivalent to `%l`.

PATTERN ITEM                                                *lua-patternitem*

A pattern item may be

   - a single character class, which matches any single character in the
      class;
   - a single character class followed by `*`, which matches 0 or more
      repetitions of characters in the class. These repetition items will
      always match the longest possible sequence;
   - a single character class followed by `+`, which matches 1 or more
      repetitions of characters in the class. These repetition items will
      always match the longest possible sequence;
                                                               *lua-nongreedy*
   - a single character class followed by `-`, which also matches 0 or
      more repetitions of characters in the class. Unlike `*`, these
      repetition items will always match the shortest possible sequence;
   - a single character class followed by `?`, which matches 0 or 1
      occurrences of a character in the class;
   - `%n`, for `n` between 1 and 9; such item matches a substring equal to the
      `n` -th captured string (see below);
   - `%bxy`, where `x` and `y` are two distinct characters; such item matches
      strings that start with `x`, end with `y`, and where the `x` and `y`
      are balanced. This means that, if one reads the string from left to
      right, counting `+1` for an `x` and `-1` for a `y`, the ending `y` is the first
      `y` where the count reaches 0. For instance, the item `%b()` matches
      expressions with balanced parentheses.

PATTERN

A pattern is a sequence of pattern items. A `^` at the beginning of a pattern
anchors the match at the beginning of the subject string. A `$` at the end of
a pattern anchors the match at the end of the subject string. At other
positions, `^` and `$` have no special meaning and represent themselves.

CAPTURES                                                        *lua-capture*

A pattern may