### Example Usage of Deriving.Args

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Deriving/Args/index.html

An example demonstrating how to use `Deriving.Args` functions and the `+>` operator to define a sequence of arguments.

```APIDOC
Deriving.Args.(<0xC2><0xA0>
  empty
  +> arg_option "foo" (estring __)
  +> arg_option "bar" (pack2 (eint __ ** eint __))
  +> flag "dotdotdot")
```

--------------------------------

### Example: Collecting String Constants

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_traverse/index.html

An example demonstrating how to use `Ast_traverse.fold` to collect all string constants from an AST.

```APIDOC
## Example: Collecting String Constants

This example shows how to inherit from `Ast_traverse.fold` to traverse an AST and collect all string constants.

```ocaml
let string_constants_of = 
  object
    inherit [string list] Ast_traverse.fold as super

    method! expression e acc = 
      let acc = super#expression e acc in
      match e.pexp_desc with 
      | Pexp_constant (Const_string (s, _)) -> s :: acc
      | _ -> acc

    method! pattern p acc = 
      let acc = super#pattern p acc in
      match p.ppat_desc with 
      | Ppat_constant (Const_string (s, _)) -> s :: acc
      | _ -> acc
  end

let string_constants_of_structure = string_constants_of#structure
```
```

--------------------------------

### Function f Usage Example

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/matching-code.html

Example of calling the composed function 'f' with a string 'name' and an expression, showing the successful result.

```ocaml
f "name" [%expr ()] ;;
```

--------------------------------

### Example of estring with __'

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_pattern/index.html

Demonstrates the usage of `__'` pattern to capture a string constant along with its location.

```ocaml
estring __'
```

--------------------------------

### Pexp_unreachable Example

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/index.html

Represents an unreachable code path in the AST.

```ocaml
| Pexp_unreachable
```

--------------------------------

### Example of attribute matching with longest match rule

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Attribute/index.html

Illustrates how Ppxlib selects the longest matching attribute when multiple are possible. This example shows a specific `@foo.default 0` attribute being matched.

```ocaml
type t = { x : int [@default 42] [@foo.default 0] }
```

--------------------------------

### Extender Example with [%yojson]

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/driver.html

Demonstrates an extender transformation that rewrites a DSL-like syntax within an extension node into OCaml code. This is useful for generating values from custom syntaxes.

```ocaml
  let json =
    [%yojson
      [ { name = "Anne"; grades = ["A"; "B-"; "B+"] }
      ; { name = "Bernard"; grades = ["B+"; "A"; "B-"] }
      ]
    ]

```

```ocaml
  let json =
    `List
      [ `Assoc
          [ ("name", `String "Anne")
          ; ("grades", `List [`String "A"; `String "B-"; `String "B+"])
          ]
      ; `Assoc
          [ ("name", `String "Bernard")
          ; ("grades", `List [`String "B+"; `String "A"; `String "B-"])
          ]
      ]

```

--------------------------------

### Pexp_extension Example

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/index.html

Illustrates the `Pexp_extension` constructor for representing extension nodes in the AST, typically used for ppx syntax like `[%id]`.

```ocaml
| Pexp_extension of extension
```

--------------------------------

### Example of pair with eint and __'

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_pattern/index.html

Illustrates a case where using `__'` with `pair` and `eint` might not yield the expected result, suggesting alternatives like using `pexp_loc`.

```ocaml
pair (eint (int 42)) __'
```

--------------------------------

### Apply an Extender

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/writing-ppxs.html

An example of applying a custom extender using the `[%add_suffix ...]` syntax. This demonstrates how the registered extender transforms the code.

```ocaml
let () = print_endline [%add_suffix "helloworld"]
```

--------------------------------

### Lift Traversal Example

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/ast-traversal.html

Illustrates a 'lift' traversal for a simple tree structure, transforming a Parsetree value into one of another type in a bottom-up manner.

```ocaml
let lift ~f = function
    Leaf a -> f.leaf a
  | Node(a,x,y) -> f.node a (lift ~f x) (lift ~f y)

```

--------------------------------

### create

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Stdppx/Out_channel/index.html

Creates a new output channel. Allows configuration of binary mode, append mode, existence check, and permissions.

```APIDOC
## create

### Description
Creates a new output channel with customizable options.

### Signature
`val create : ?binary:bool -> ?append:bool -> ?fail_if_exists:bool -> ?perm:int -> string -> Stdlib.out_channel`

### Parameters
- `?binary` (bool) - Optional: If true, opens the channel in binary mode.
- `?append` (bool) - Optional: If true, appends to the file if it exists.
- `?fail_if_exists` (bool) - Optional: If true, raises an error if the file already exists.
- `?perm` (int) - Optional: File permissions.
- `string` - The filename to open.

### Returns
`Stdlib.out_channel` - The created output channel.
```

--------------------------------

### Multiple Newtype Parameters Example

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/index.html

Shows how multiple `Pparam_newtype` nodes are used to represent multiple type parameters in a function signature, such as `(type a b c)`. Each parameter gets its own node with associated location information.

```ocaml
[
  { pparam_kind = Pparam_newtype a; pparam_loc = loc1 };
  { pparam_kind = Pparam_newtype b; pparam_loc = loc2 };
  { pparam_kind = Pparam_newtype c; pparam_loc = loc3 };
]
```

--------------------------------

### Expand Environment Variables with ppx_get_env

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/examples.html

This PPX extension expands `[%get_env "VAR_NAME"]` into the string value of the environment variable `VAR_NAME` at compile time. It's a toy example and has limitations with build systems like Dune due to its reliance on environment variables.

```ocaml
let () = print_string [%get_env "foo"]
```

```ocaml
let () = print_string "foo"
```

```ocaml
open Ppxlib

let expand ~ctxt env_var = 
  let loc = Expansion_context.Extension.extension_point_loc ctxt in
  match Sys.getenv env_var with 
  | value -> Ast_builder.Default.estring ~loc value
  | exception Not_found ->
      let ext = 
        Location.error_extensionf ~loc "The environment variable %s is unbound" 
          env_var
      in 
      Ast_builder.Default.pexp_extension ~loc ext

let my_extension = 
  Extension.V3.declare "get_env" Extension.Context.expression 
    Ast_pattern.(single_expr_payload (estring __)) 
    expand

let rule = Ppxlib.Context_free.Rule.extension my_extension
let () = Driver.register_transformation ~rules:[ rule ] "get_env"
```

--------------------------------

### Basic AST Map Traversal

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/ast-traversal.html

Demonstrates the basic usage of the Ast_traverse.map class to create an identity map for a payload. This serves as a starting point for custom traversals.

```ocaml
let f payload =
  let map = new Ppxlib.Ast_traverse.map in
  map#payload ;;

```

--------------------------------

### Create a Quoter in OCaml

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/good-practices.html

Initialize a quoter instance using `Quoter.create`. This is the first step in using ppxlib's quoting mechanism.

```ocaml
# open Expansion_helper ;;
#s let quoter = Quoter.create () ;;
val quoter : Quoter.t = <abstr>
```

--------------------------------

### Implement a Debug Rewriter with Quoting

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/good-practices.html

An example of a `debug` rewriter that uses `ppxlib`'s quoting mechanism to handle variable names safely. It includes creating a quoter, an AST mapper to replace variables with quoted versions, and sanitizing the final expression.

```ocaml
# let rewrite expr =
    (* Create a quoter *)
    let quoter = Quoter.create () in
    (* An AST mapper to log and replace variables with quoted ones *)
    let replace_var = 
      object
        (* See the chapter on AST traverse *)
        inherit Ast_traverse.map as super

        (* in case of expression *)
        method! expression expr = 
          match expr.pexp_desc with 
          (* in case of identifier (not "+") *)
          | Pexp_ident { txt = Lident var_name; loc } 
            when not (String.equal "+" var_name) -> 
              (* quote the var *)
              let quoted_var = Quoter.quote quoter expr in 
              let name = Ast_builder.Default.estring ~loc var_name in 
              (* and rewrite the expression *)
              [%expr
                debug [%e name] [%e quoted_var];
                [%e quoted_var]]
          (* otherwise, continue inside recursively *)
          | _ -> super#expression expr
      end
    in 
    let quoted_rewrite = replace_var#expression expr in 
    let loc = expr.pexp_loc in 
    (* Sanitize the whole thing *)
    Quoter.sanitize quoter 
      [%expr 
        let debug = Printf.printf "%s = %d; " in 
        [%e quoted_rewrite]] ;;
val rewrite : expression -> expression = <fun>
```

--------------------------------

### create

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Stdppx/In_channel/index.html

Creates an input channel from a string. Optionally, it can be opened in binary mode.

```APIDOC
## create

### Description
Creates an input channel from a string. Optionally, it can be opened in binary mode.

### Signature
`val create : ?binary:bool -> string -> Stdlib.in_channel`

### Parameters
- `binary` (bool) - Optional. If true, opens the channel in binary mode.
- `string` (string) - The string to create the input channel from.
```

--------------------------------

### Example of a non-recursive type approximated as recursive

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/class-type_is_recursive/index.html

This example demonstrates a scenario where a type `t` is defined using a module alias, leading `type_is_recursive` to incorrectly identify it as recursive. This highlights the approximation nature of the class.

```ocaml
  module M = struct
    type t = Foo
  end

  type t = M.(t)

```

--------------------------------

### set_filename

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Location/index.html

Updates the filename in both the start and end positions of a location.

```APIDOC
val set_filename : t -> string -> t
```

--------------------------------

### Get Location

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_builder/Default/Located/index.html

Extracts the `Location.t` associated with a located value.

```APIDOC
val loc : _ t -> Location.t
```

--------------------------------

### init

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Location/index.html

Initializes a lexer buffer with the filename and line number of a given file.

```APIDOC
val init : Stdlib.Lexing.lexbuf -> string -> unit
```

--------------------------------

### Pp_ast.Config.make

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Pp_ast/Config/index.html

Creates a custom configuration for pretty-printing ASTs. Allows customization of attribute visibility, location display, and location formatting.

```APIDOC
## Pp_ast.Config.make

### Description
Creates a custom pretty-printing configuration for ASTs. This function allows fine-grained control over how ASTs are displayed, including whether attributes and locations are shown, and how locations are formatted.

### Signature
`val make : ?show_attrs:bool -> ?show_locs:bool -> ?loc_mode:[ `Short | `Full ] -> ?printer:repr pp -> unit -> t`

### Parameters
#### Optional Parameters
- **?show_attrs** (bool) - Controls whether attributes are shown or hidden. Defaults to `false`.
- **?show_locs** (bool) - Controls whether locations are shown or hidden. Defaults to `false`.
- **?loc_mode** (`Short` | `Full`) - Controls how locations are displayed if they are shown. Defaults to ``Short`.
  - ``Short`: Displays locations as `"l1c6..l2c2"` for multiline, `"l1c6..12"` for single line. Ghost locations are suffixed with `"(g)"`.
  - ``Full`: Displays locations like any other record.
- **?printer** (repr pp) - A custom printer function.

### Returns
- **t** - A pretty-printing configuration object.
```

--------------------------------

### Get Extension

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Extension/Context/index.html

Retrieves the extension associated with a given AST node.

```APIDOC
val get_extension : 'a t -> 'a -> ((string Astlib.Location.loc * Astlib.Ast_502.Parsetree.payload) * Astlib.Ast_502.Parsetree.attribute list) option
```

--------------------------------

### location

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_pattern/index.html

Matches a location by its start position, end position, and ghost flag.

```APIDOC
## location

### Description
Matches a location by its start position, end position, and ghost flag.

### Signature
```
val location :    start:(Stdlib.Lexing.position, 'a, 'b) Ppxlib__.Ast_pattern0.t -> end_:(Stdlib.Lexing.position, 'b, 'c) Ppxlib__.Ast_pattern0.t -> ghost:(bool, 'c, 'd) Ppxlib__.Ast_pattern0.t -> (Astlib.Location.t, 'a, 'd) Ppxlib__.Ast_pattern0.t
```
```

--------------------------------

### Get Head Element (hd)

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Stdppx/NonEmptyList/index.html

Retrieves the head element of a non-empty list.

```APIDOC
val hd : ('a * 'b) -> 'a
```

--------------------------------

### standalone

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Driver/index.html

Configures the driver to be suitable for use with `-pp` or as a standalone command-line tool.

```APIDOC
## standalone

### Description
Suitable for -pp and also usable as a standalone command line tool.

### Signature
`val standalone : unit -> unit`
```

--------------------------------

### Generated Pattern Structure

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/matching-code.html

This is an example of the OCaml AST structure generated by Metaquot for a pattern.

```ocaml
    {
      pexp_desc =
        (Pexp_apply
           ({ 
              pexp_desc = (Pexp_ident { txt = (Lident "+"); loc = _ });
              pexp_loc = _;
              pexp_attributes = _
            },
             [(Nolabel,
                {
                  pexp_desc = (Pexp_constant (Pconst_integer ("1", None)));
                  pexp_loc = _;
                  pexp_attributes = _
                });
             (Nolabel,
               {
                 pexp_desc = (Pexp_constant (Pconst_integer ("1", None)));
                 pexp_loc = _;
                 pexp_attributes = _
               })]));
      pexp_loc = _;
      pexp_attributes = _
    }
```

--------------------------------

### Deriving.Args.empty

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Deriving/Args/index.html

Represents an empty set of arguments, serving as a starting point for argument definitions.

```APIDOC
val empty : ('m, 'm) t
```

--------------------------------

### apply_keyword_edition

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Astlib/Keyword/index.html

Processes keyword settings from environment variables and CLI options, initializing the compiler's lexer.

```APIDOC
## apply_keyword_edition

### Description
Processes any keywords= sections from the OCAMLPARAM environment variable and CLI option and initialises the compiler's lexer with the correct keyword set.

### Signature
`val apply_keyword_edition : cli:string option -> unit -> unit`
```

--------------------------------

### Error Message Access and Modification

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Location/Error/index.html

Functions to get and set the message associated with an error.

```APIDOC
## `Location.Error.message`

### Description
Retrieves the primary message string from an error.

### Signature
`val message : t -> string`

## `Location.Error.set_message`

### Description
Updates the primary message string of an existing error.

### Signature
`val set_message : t -> string -> t`
```

--------------------------------

### Construct Open Infos: Fresh

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_builder/Default/index.html

Use `open_infos` with `Fresh` to construct an `Ast.open_infos` node representing `open X`, creating a fresh namespace.

```ocaml
open  X
```

--------------------------------

### get

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Caller_id/index.html

Retrieves the location of the caller, optionally skipping specified strings in the call stack.

```APIDOC
## get

### Description
Retrieves the location of the caller, optionally skipping specified strings in the call stack.

### Signature
`val get : skip:string list -> Stdlib__Printexc.location option`

### Parameters
#### skip
- **skip** (string list) - A list of strings to filter out from the call stack when determining the caller's location.

### Returns
- `Stdlib__Printexc.location option` - An option containing the caller's location if found, otherwise `None`.
```

--------------------------------

### Getting the Name of a Floating Attribute

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Attribute/Floating/index.html

Retrieves the string name of a declared floating attribute.

```APIDOC
## `name`

### Description
Returns the name of the floating attribute.

### Signature
`val name : (_, _) t -> string`
```

--------------------------------

### Constructor Argument Patterns

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_pattern/index.html

Patterns for matching constructor arguments.

```APIDOC
## pcstr_tuple

### Description
Pattern for matching a tuple constructor argument.

### Signature
```
val pcstr_tuple : (Astlib.Ast_502.Parsetree.core_type list, 'a, 'b) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.constructor_arguments, 'a, 'b) Ppxlib__.Ast_pattern0.t
```
```

```APIDOC
## pcstr_record

### Description
Pattern for matching a record constructor argument.

### Signature
```
val pcstr_record : (Astlib.Ast_502.Parsetree.label_declaration list, 'a, 'b) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.constructor_arguments, 'a, 'b) Ppxlib__.Ast_pattern0.t
```
```

--------------------------------

### Get Name of Longident

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Longident/index.html

Extracts the string name from a `Longident.t`. For `Ldot (t, s)`, it returns `s`. For `Lident s`, it returns `s`.

```APIDOC
val name : t -> string
```

--------------------------------

### String Creation and Initialization

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Stdppx/String/index.html

Functions for creating and initializing strings.

```APIDOC
## String Creation and Initialization

### `make`

Creates a string of a given length, filled with a specified character.

- **Signature**: `val make : int -> char -> string`

### `init`

Creates a string of a given length by applying a function to each index.

- **Signature**: `val init : int -> f:(int -> char) -> string`

### `empty`

Represents an empty string.

- **Signature**: `val empty : string`
```

--------------------------------

### pexp_letmodule

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_pattern/index.html

Matches a let-module binding.

```APIDOC
## pexp_letmodule

### Description
Matches a let-module binding.

### Signature
`val pexp_letmodule : (string option, 'a, 'b) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.module_expr, 'b, 'c) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.expression, 'c, 'd) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.expression, 'a, 'd) Ppxlib__.Ast_pattern0.t`
```

--------------------------------

### Prefix and Suffix Checks

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Stdppx/Bytes/index.html

Functions for checking if a bytes sequence starts or ends with a given prefix or suffix.

```APIDOC
## starts_with

### Description
Checks if a bytes sequence starts with a given prefix.

### Parameters
#### Path Parameters
- **prefix** (bytes) - The prefix to check for.

### Method
val starts_with : prefix:bytes -> bytes -> bool

## ends_with

### Description
Checks if a bytes sequence ends with a given suffix.

### Parameters
#### Path Parameters
- **suffix** (bytes) - The suffix to check for.

### Method
val ends_with : suffix:bytes -> bytes -> bool
```

--------------------------------

### Extension and Extension Constructor Conversions

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Astlib/Migrate_504_503/index.html

Functions for copying extensions and extension constructors.

```APIDOC
## copy_extension

### Description
Copies an extension from Ast_504 to Ast_503.

### Signature
`val copy_extension : Ast_504.Parsetree.extension -> Ast_503.Parsetree.extension`

## copy_extension_constructor

### Description
Copies an extension constructor from Ast_504 to Ast_503.

### Signature
`val copy_extension_constructor : Ast_504.Parsetree.extension_constructor -> Ast_503.Parsetree.extension_constructor`

## copy_extension_constructor_kind

### Description
Copies the kind of an extension constructor from Ast_504 to Ast_503.

### Signature
`val copy_extension_constructor_kind : Ast_504.Parsetree.extension_constructor_kind -> Ast_503.Parsetree.extension_constructor_kind`
```

--------------------------------

### Location Type Definition

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Location/index.html

Defines the structure of a location, including start and end positions and a ghost flag.

```APIDOC
type t = Astlib.Location.t = {
  loc_start : Stdlib.Lexing.position;
  loc_end : Stdlib.Lexing.position;
  loc_ghost : bool;
}
```

--------------------------------

### plist

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_builder/Default/index.html

Builds a pattern for a list.

```APIDOC
## plist

### Description
`plist ~loc [pat1; pat2; pat3]` produces the list pattern `[pat1; pat2; pat3]`.

### Signature
`val plist : loc:Location.t -> Astlib.Ast_502.Parsetree.pattern list -> Astlib.Ast_502.Parsetree.pattern`
```

--------------------------------

### Attribute Retrieval

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Attribute/index.html

Functions for getting attribute values, with options for error handling and marking attributes as seen.

```APIDOC
## `get_res`

### Description
Retrieves the value of an attribute. Returns a `result` type, which can be `Ok` with the attribute's value or `Error` with a list of location errors if the attribute is duplicated.

### Signature
`val get_res : ('a, 'b) t -> ?mark_as_seen:bool -> 'a -> ('b option, Location.Error.t Stdppx.NonEmptyList.t) Stdlib.result`

### Parameters
- `?mark_as_seen` (bool): If true (default), marks the attribute as seen. If false, it does not.
- The first argument is the attribute to retrieve.
- The second argument is the item to search for the attribute on.
```

```APIDOC
## `get`

### Description
Retrieves the value of an attribute. Similar to `get_res`, but raises a located error if the attribute is duplicated.

### Signature
`val get : ('a, 'b) t -> ?mark_as_seen:bool -> 'a -> 'b option`
```

```APIDOC
## `has_flag_res`

### Description
Checks if a flag attribute is present. Returns a `result` type indicating success or a list of location errors.

### Signature
`val has_flag_res : 'a flag -> ?mark_as_seen:bool -> 'a -> (bool, Location.Error.t Stdppx.NonEmptyList.t) Stdlib.result`
```

```APIDOC
## `has_flag`

### Description
Checks if a flag attribute is present. Raises a located error if the attribute is duplicated.

### Signature
`val has_flag : 'a flag -> ?mark_as_seen:bool -> 'a -> bool`
```

--------------------------------

### Module Type Constraints in Ppxlib

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/index.html

Illustrates different ways to specify module type constraints using Ppxlib's syntax, including `Pwith_modtype`, `Pwith_modtypesubst`, `Pwith_typesubst`, and `Pwith_modsubst`.

```ocaml
(* `with module type X.Y = Z` *)
```

```ocaml
(* `with module type X.Y := sig end` *)
```

```ocaml
(* `with type X.t := ..., same format as [Pwith_type]` *)
```

```ocaml
(* `with module X.Y := Z` *)
```

--------------------------------

### add_simple_handler

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Driver/Cookies/index.html

A shorthand for registering a handler that gets a specific cookie and passes its parsed value to a callback function.

```APIDOC
## add_simple_handler

### Description
A shorthand for registering a handler that gets a specific cookie and passes its parsed value to a callback function.

### Signature
`val add_simple_handler : string -> (Astlib.Ast_502.Parsetree.expression, 'a -> 'a, 'b) Ast_pattern.t -> f:('b option -> unit) -> unit`

### Parameters
- `name` (string): The name of the cookie to retrieve.
- `pattern` ((Astlib.Ast_502.Parsetree.expression, 'a -> 'a, 'b) Ast_pattern.t): The pattern to parse the cookie value.
- `f` (('b option -> unit)): The callback function that receives the parsed cookie value (or None if not found).
```

--------------------------------

### with_file

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Stdppx/Out_channel/index.html

Opens a file, performs an action with the output channel, and ensures the channel is closed afterward.

```APIDOC
## with_file

### Description
Opens a file, applies a function to its output channel, and ensures proper closure.

### Signature
`val with_file : ?binary:bool -> ?append:bool -> ?fail_if_exists:bool -> ?perm:int -> string -> f:(Stdlib.out_channel -> 'a) -> 'a`

### Parameters
- `?binary` (bool) - Optional: If true, opens the channel in binary mode.
- `?append` (bool) - Optional: If true, appends to the file if it exists.
- `?fail_if_exists` (bool) - Optional: If true, raises an error if the file already exists.
- `?perm` (int) - Optional: File permissions.
- `string` - The filename to open.
- `f` (Stdlib.out_channel -> 'a) - The function to apply to the output channel.

### Returns
`'a` - The result of the function `f`.
```

--------------------------------

### Construct Ptyp_alias Core Type

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_builder/Default/index.html

Use `ptyp_alias` to construct a `Ptyp_alias` node, representing type aliases. Example: `T as 'a`.

```ocaml
val ptyp_alias :    loc:Location.t -> Astlib.Ast_502.Parsetree.core_type -> string Astlib.Location.loc -> Astlib.Ast_502.Parsetree.core_type
```

--------------------------------

### Driver.Create_file_property.set

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Driver/Create_file_property/index.html

Sets a file property. If the `-output-metadata FILE` option is used, this information will be written to the specified file.

```APIDOC
## `val set : T.t -> unit`

### Description
Sets a file property. This function is used to record a piece of information about a file that can be passed to the build system via metadata output.

### Parameters
- `T.t`: The file property to set.
```

--------------------------------

### Create Unit Expression and Pattern AST Nodes

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_builder/Make/index.html

Use `eunit` to create an AST node for the unit expression `()` and `punit` for the unit pattern.

```ocaml
val eunit : Astlib.Ast_502.Parsetree.expression
val punit : Astlib.Ast_502.Parsetree.pattern
```

--------------------------------

### Define Empty Deriver Dependencies

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/writing-ppxs.html

An example of initializing deriver dependencies as an empty list. This indicates that the deriver has no prerequisites.

```ocaml
let deps = [] ;;
```

--------------------------------

### Standalone Driver Usage

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/driver.html

This is the general command-line format for a standalone driver. It accepts extra arguments and can process one or more OCaml files.

```bash
driver.exe [extra_args] [<files>]
```

--------------------------------

### Construct OCaml Location

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_builder/Make/index.html

Use `location` to construct an Ast location with start and end positions and a ghost flag.

```OCaml
Stdlib.Lexing.dummy_pos, Stdlib.Lexing.dummy_pos, false
```

--------------------------------

### Construct Open Infos: Override

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_builder/Default/index.html

Use `open_infos` with `Override` to construct an `Ast.open_infos` node representing `open! X`, which silences shadowing warnings.

```ocaml
open! X
```

--------------------------------

### Location Type

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Astlib/Location/index.html

Defines the structure for source code locations, including start and end positions and a ghost flag.

```APIDOC
## type t

### Description
Represents a source code location, defined by start and end positions, and a boolean indicating if it's a ghost location.

### Fields
- **loc_start** (Stdlib.Lexing.position) - The starting position of the location.
- **loc_end** (Stdlib.Lexing.position) - The ending position of the location.
- **loc_ghost** (bool) - A flag indicating if the location is a ghost location.
```

--------------------------------

### fresh

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_pattern/index.html

Pattern for matching a fresh override flag.

```APIDOC
## fresh

### Description
Matches a fresh override flag.

### Type Signature
```
(Astlib.Ast_502.Asttypes.override_flag, 'a, 'a) Ppxlib__.Ast_pattern0.t
```
```

--------------------------------

### get

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Driver/Cookies/index.html

Looks for a cookie by name and parses its value using a provided pattern. Raises an error if parsing fails.

```APIDOC
## get

### Description
Looks for a cookie by name and parses its value using a provided pattern. Raises an error if parsing fails.

### Signature
`val get : t -> string -> (Astlib.Ast_502.Parsetree.expression, 'a -> 'a, 'b) Ast_pattern.t -> 'b option`

### Parameters
- `cookies` (t): The cookie collection to search within.
- `name` (string): The name of the cookie to find.
- `pattern` ((Astlib.Ast_502.Parsetree.expression, 'a -> 'a, 'b) Ast_pattern.t): The pattern to use for parsing the cookie's value.
```

--------------------------------

### Construct Ptyp_package Core Type

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_builder/Default/index.html

Use `ptyp_package` to construct a `Ptyp_package` node for type package declarations. Example: `(module S)`.

```ocaml
val ptyp_package :    loc:Location.t -> (Astlib.Longident.t Astlib.Location.loc    * (Astlib.Longident.t Astlib.Location.loc       * Astlib.Ast_502.Parsetree.core_type)        list) -> Astlib.Ast_502.Parsetree.core_type
```

--------------------------------

### make

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Deriving/Generator/V2/index.html

Creates a generator that has access to the expansion context. This allows the generator to query information about the current expansion, such as the compiler's version or the target environment.

```APIDOC
## make

### Description
Creates a generator with access to the expansion context.

### Signature
`val make : ?attributes:Attribute.packed list -> ?deps:t list -> ?unused_code_warnings:bool -> ('f, 'output_ast) Args.t -> (ctxt:Expansion_context.Deriver.t -> 'input_ast -> 'f) -> ('output_ast, 'input_ast) t`
```

--------------------------------

### Constructor Declaration Patterns

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_pattern/index.html

Patterns for matching constructor declarations.

```APIDOC
## constructor_declaration_attributes

### Description
Pattern for matching the attributes of a constructor declaration.

### Signature
```
val constructor_declaration_attributes : (Astlib.Ast_502.Parsetree.attribute list, 'a, 'b) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.constructor_declaration, 'b, 'c) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.constructor_declaration, 'a, 'c) Ppxlib__.Ast_pattern0.t
```
```

```APIDOC
## constructor_declaration

### Description
Pattern for matching a full constructor declaration.

### Signature
```
val constructor_declaration : name:(string, 'a, 'b) Ppxlib__.Ast_pattern0.t -> vars:(string Astlib.Location.loc list, 'b, 'c) Ppxlib__.Ast_pattern0.t -> args:     (Astlib.Ast_502.Parsetree.constructor_arguments, 'c, 'd) Ppxlib__.Ast_pattern0.t -> res:     (Astlib.Ast_502.Parsetree.core_type option, 'd, 'e) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.constructor_declaration, 'a, 'e) Ppxlib__.Ast_pattern0.t
```
```

--------------------------------

### Construct Ptyp_extension Core Type

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_builder/Default/index.html

Use `ptyp_extension` to construct a `Ptyp_extension` node in the OCaml type system. Example: `[%id]`.

```ocaml
val ptyp_extension :    loc:Location.t -> (string Astlib.Location.loc * Astlib.Ast_502.Parsetree.payload) -> Astlib.Ast_502.Parsetree.core_type
```

--------------------------------

### copy_extension_constructor

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Astlib/Migrate_409_408/index.html

Copies an extension constructor from Ast_409.Parsetree to Ast_408.Parsetree.

```APIDOC
## copy_extension_constructor

### Description
Copies an extension constructor from OCaml 4.09 AST to 4.08 AST.

### Parameters
- `ec`: The `Ast_409.Parsetree.extension_constructor` to copy.

### Returns
A `Ast_408.Parsetree.extension_constructor` representing the copied structure.
```

--------------------------------

### Get Last Component of Longident

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Longident/index.html

Retrieves the last string component of a longident. Raises an exception if the longident is empty or invalid.

```APIDOC
val last_exn : t -> string
```

--------------------------------

### Construct Ptyp_open Core Type

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_builder/Default/index.html

Use `ptyp_open` to construct a `Ptyp_open` node, representing module type openings. Example: `M.(T)`.

```ocaml
val ptyp_open :    loc:Location.t -> Astlib.Longident.t Astlib.Location.loc -> Astlib.Ast_502.Parsetree.core_type -> Astlib.Ast_502.Parsetree.core_type
```

--------------------------------

### Class `Ast.lift_map_with_context` Methods

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib_ast/Ast/class-lift_map_with_context/index.html

The `Ast.lift_map_with_context` class provides methods to traverse and transform Abstract Syntax Tree (AST) nodes while carrying a context. Each method takes a context and an AST node, returning the transformed AST node and the updated context.

```APIDOC
## Class `Ast.lift_map_with_context`

This class provides methods for traversing and transforming AST nodes with a context.

### Methods

- `class_field : 'ctx -> class_field -> class_field * 'res`
- `class_field_desc : 'ctx -> class_field_desc -> class_field_desc * 'res`
- `class_field_kind : 'ctx -> class_field_kind -> class_field_kind * 'res`
- `class_declaration : 'ctx -> class_declaration -> class_declaration * 'res`
- `module_type : 'ctx -> module_type -> module_type * 'res`
- `module_type_desc : 'ctx -> module_type_desc -> module_type_desc * 'res`
- `functor_parameter : 'ctx -> functor_parameter -> functor_parameter * 'res`
- `signature : 'ctx -> signature -> signature * 'res`
- `signature_item : 'ctx -> signature_item -> signature_item * 'res`
- `signature_item_desc : 'ctx -> signature_item_desc -> signature_item_desc * 'res`
- `module_declaration : 'ctx -> module_declaration -> module_declaration * 'res`
- `module_substitution : 'ctx -> module_substitution -> module_substitution * 'res`
- `module_type_declaration : 'ctx -> module_type_declaration -> module_type_declaration * 'res`
- `open_infos : 'a. ('ctx -> 'a -> 'a * 'res) -> 'ctx -> 'a open_infos -> 'a open_infos * 'res`
- `open_description : 'ctx -> open_description -> open_description * 'res`
- `open_declaration : 'ctx -> open_declaration -> open_declaration * 'res`
- `include_infos : 'a. ('ctx -> 'a -> 'a * 'res) -> 'ctx -> 'a include_infos -> 'a include_infos * 'res`
- `include_description : 'ctx -> include_description -> include_description * 'res`
- `include_declaration : 'ctx -> include_declaration -> include_declaration * 'res`
- `with_constraint : 'ctx -> with_constraint -> with_constraint * 'res`
- `module_expr : 'ctx -> module_expr -> module_expr * 'res`
- `module_expr_desc : 'ctx -> module_expr_desc -> module_expr_desc * 'res`
- `structure : 'ctx -> structure -> structure * 'res`
- `structure_item : 'ctx -> structure_item -> structure_item * 'res`
- `structure_item_desc : 'ctx -> structure_item_desc -> structure_item_desc * 'res`
- `value_constraint : 'ctx -> value_constraint -> value_constraint * 'res`
- `value_binding : 'ctx -> value_binding -> value_binding * 'res`
- `module_binding : 'ctx -> module_binding -> module_binding * 'res`
- `toplevel_phrase : 'ctx -> toplevel_phrase -> toplevel_phrase * 'res`
- `toplevel_directive : 'ctx -> toplevel_directive -> toplevel_directive * 'res`
- `directive_argument : 'ctx -> directive_argument -> directive_argument * 'res`
- `directive_argument_desc : 'ctx -> directive_argument_desc -> directive_argument_desc * 'res`
- `cases : 'ctx -> cases -> cases * 'res`
```

--------------------------------

### Deriver with Standard Attributes

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/writing-ppxs.html

Example of using the `deriving` attribute to automatically generate implementations for standard functions like `show` and `yojson`.

```ocaml
type tree = Leaf | Node of tree * tree  [@@deriving show, yojson]
```

--------------------------------

### Class Ast_traverse.map_with_expansion_context_and_errors

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_traverse/class-map_with_expansion_context_and_errors/index.html

This class inherits from `Ppxlib_traverse_builtins.std_lift_mappers_with_context` and `Ppxlib_ast.Ast.lift_map_with_context`, providing a framework for AST mapping operations that manage expansion contexts and accumulate errors.

```APIDOC
## Class `Ast_traverse.map_with_expansion_context_and_errors`

This class provides functionality for traversing and mapping Abstract Syntax Trees (ASTs) while managing expansion contexts and collecting errors. It inherits from standard traversal utilities to offer a robust mechanism for complex transformations.

### Inheritance

- `inherit [Ppxlib__.Expansion_context.Base.t, Ppxlib__.Location.Error.t list] Ppxlib_traverse_builtins.std_lift_mappers_with_context`
- `inherit [Ppxlib__.Expansion_context.Base.t, Ppxlib__.Location.Error.t list]           Ppxlib_ast.Ast.lift_map_with_context`

### Purpose

The primary purpose of this class is to facilitate AST transformations where each step of the traversal needs to be aware of the current expansion context and where errors encountered during the transformation should be collected and reported.
```

--------------------------------

### Basic Patterns

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_pattern/index.html

Core patterns for capturing, dropping, and creating alternatives.

```APIDOC
## `__`

### Description
Pattern that captures its input.

### Signature
val __ : ('a, 'a -> 'b, 'b) t

## `__'`

### Description
Same as `__` but also captures the location. Should only be used for types that do not embed a location.

### Signature
val __' : ('a, 'a Loc.t -> 'b, 'b) t

## `drop`

### Description
Useful when some part of the AST is irrelevant. The captured value is ignored.

### Signature
val drop : ('a, 'b, 'b) t

## `alt`

### Description
Matches either the first pattern or the second one.

### Signature
val alt : ('a, 'b, 'c) t -> ('a, 'b, 'c) t -> ('a, 'b, 'c) t

## `(|||)`

### Description
Same as `alt`.

### Signature
val (|||) : ('a, 'b, 'c) t -> ('a, 'b, 'c) t -> ('a, 'b, 'c) t

## `alt_option`

### Description
Same as `alt`, for the common case where the left-hand-side captures a value but not the right-hand-side.

### Signature
val alt_option : ('a, 'v -> 'b, 'c) t -> ('a, 'b, 'c) t -> ('a, 'v option -> 'b, 'c) t
```

--------------------------------

### Extension Constructor Migration

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Astlib/Migrate_414_413/index.html

Copies an extension constructor from OCaml 4.14 AST to 4.13 AST.

```APIDOC
## copy_extension_constructor

### Description
Copies an extension constructor from OCaml 4.14 AST to 4.13 AST.

### Signature
`val copy_extension_constructor : Ast_414.Parsetree.extension_constructor -> Ast_413.Parsetree.extension_constructor`
```

--------------------------------

### Construct Location AST Node

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_builder/Default/index.html

Use `location` to construct an `Ast.location` node, specifying start and end positions and a ghost flag.

```ocaml
val location :    start:Stdlib.Lexing.position -> end_:Stdlib.Lexing.position -> ghost:bool -> Astlib.Location.t
```

--------------------------------

### create

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Ast_pattern/Packed/index.html

Creates a packed AST pattern. It takes a base pattern and a value, returning a new packed pattern.

```APIDOC
## create

### Description
Creates a packed AST pattern.

### Signature
`val create : ('a, 'b, 'c) t -> 'b -> ('a, 'c) t`
```

--------------------------------

### Get attribute value

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Attribute/index.html

A convenience function over `get_res` that raises a located error if the attribute is duplicated. Returns `None` if the attribute is not found.

```ocaml
val get : ('a, 'b) t -> ?mark_as_seen:bool -> 'a -> 'b option
```

--------------------------------

### UTF-8 Character Handling

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Stdppx/Bytes/index.html

Functions for getting and setting UTF-8 encoded characters within bytes sequences, and checking for valid UTF-8 encoding.

```APIDOC
## get_utf_8_uchar

### Description
Gets a UTF-8 encoded Unicode character from a bytes sequence at a given byte offset.

### Parameters
#### Path Parameters
- **offset** (int) - The byte offset in the bytes sequence.

### Method
val get_utf_8_uchar : bytes -> int -> Stdlib.Uchar.utf_decode

## set_utf_8_uchar

### Description
Sets a UTF-8 encoded Unicode character in a bytes sequence at a given byte offset.

### Parameters
#### Path Parameters
- **offset** (int) - The byte offset in the bytes sequence.
- **uchar** (Stdlib.Uchar.t) - The Unicode character to set.

### Method
val set_utf_8_uchar : bytes -> int -> Stdlib.Uchar.t -> int

## is_valid_utf_8

### Description
Checks if a bytes sequence contains valid UTF-8 encoded data.

### Method
val is_valid_utf_8 : bytes -> bool
```

--------------------------------

### Add Metaquot to Dune Preprocess

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/generating-code.html

Include `ppxlib.metaquot` in your Dune stanza's `preprocess` to enable Metaquot functionality.

```dune
  (preprocess (pps ppxlib.metaquot))
```

--------------------------------

### Deriver Example with @@deriving

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/driver.html

Illustrates how a deriver attribute is used to generate appended code for a type definition. The original type definition remains unmodified.

```ocaml
  type t = Int of int | Float of float [@@deriving yojson]

  let x = ...

```

```ocaml
  type ty = Int of int | Float of float [@@deriving yojson]

  let ty_of_yojson = ...
  let ty_to_yojson = ...

  let x = ...

```

--------------------------------

### with_file

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Stdppx/In_channel/index.html

Opens a file, applies a function to its input channel, and ensures the channel is closed afterward. Supports binary mode.

```APIDOC
## with_file

### Description
Opens a file, applies a function to its input channel, and ensures the channel is closed afterward. Supports binary mode.

### Signature
`val with_file : ?binary:bool -> string -> f:(Stdlib.in_channel -> 'a) -> 'a`

### Parameters
- `binary` (bool) - Optional. If true, opens the channel in binary mode.
- `string` (string) - The path to the file.
- `f` (Stdlib.in_channel -> 'a) - A function that takes an input channel and returns a value of type 'a.
```

--------------------------------

### Extension Constructor Copy

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Astlib/Migrate_503_502/index.html

Copies an extension constructor from Ast_503.Parsetree to Ast_502.Parsetree.

```APIDOC
## copy_extension_constructor

### Description
Copies an extension constructor from OCaml 5.03 AST to OCaml 5.02 AST.

### Signature
```
val copy_extension_constructor : Ast_503.Parsetree.extension_constructor -> Ast_502.Parsetree.extension_constructor
```
```

--------------------------------

### pexp_for

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/Deriving/Args/index.html

Represents a for loop in the OCaml AST. It takes a pattern for the loop variable, a start expression, an end expression, a direction flag, and the loop body.

```APIDOC
## pexp_for

### Description
Represents a for loop in the OCaml AST.

### Signature
`val pexp_for : (Astlib.Ast_502.Parsetree.pattern, 'a, 'b) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.expression, 'b, 'c) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.expression, 'c, 'd) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Asttypes.direction_flag, 'd, 'e) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.expression, 'e, 'f) Ppxlib__.Ast_pattern0.t -> (Astlib.Ast_502.Parsetree.expression, 'a, 'f) Ppxlib__.Ast_pattern0.t`
```

--------------------------------

### Get Type Parameter Name

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Ppxlib/index.html

Safely retrieve the string identifier of a type parameter. `get_type_param_name_res` returns a result, while `get_type_param_name` raises an error on failure.

```ocaml
get_type_param_name_res tp

```

```ocaml
get_type_param_name tp

```

--------------------------------

### UTF-16LE Character Handling

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Stdppx/Bytes/index.html

Functions for getting and setting UTF-16 Little-Endian encoded characters within bytes sequences, and checking for valid UTF-16LE encoding.

```APIDOC
## get_utf_16le_uchar

### Description
Gets a UTF-16 Little-Endian encoded Unicode character from a bytes sequence at a given byte offset.

### Parameters
#### Path Parameters
- **offset** (int) - The byte offset in the bytes sequence.

### Method
val get_utf_16le_uchar : bytes -> int -> Stdlib.Uchar.utf_decode

## set_utf_16le_uchar

### Description
Sets a UTF-16 Little-Endian encoded Unicode character in a bytes sequence at a given byte offset.

### Parameters
#### Path Parameters
- **offset** (int) - The byte offset in the bytes sequence.
- **uchar** (Stdlib.Uchar.t) - The Unicode character to set.

### Method
val set_utf_16le_uchar : bytes -> int -> Stdlib.Uchar.t -> int

## is_valid_utf_16le

### Description
Checks if a bytes sequence contains valid UTF-16 Little-Endian encoded data.

### Method
val is_valid_utf_16le : bytes -> bool
```

--------------------------------

### copy_extension_constructor

Source: https://ocaml-ppx.github.io/ppxlib/ppxlib/Astlib/Migrate_411_412/index.html

Copies an extension constructor from Ast_411.Parsetree to Ast_412.Parsetree.

```APIDOC
## copy_extension_constructor

### Description
Copies an extension constructor from Ast_411.Parsetree to Ast_412.Parsetree.

### Signature
`val copy_extension_constructor : Ast_411.Parsetree.extension_constructor -> Ast_412.Parsetree.extension_constructor`
```