# Module Netencoding.Html

    module Html: sig .. end

Encodes characters that need protection by converting them to entity references. E.g. `"<"` is converted to `"&lt;"`. As the entities may be named, there is a dependency on the character set.
Legacy functions:

    val encode_from_latin1 : string -> string

    val decode_to_latin1 : string -> string

These functions have a more general interface and should be preferred in new programs.

    val unsafe_chars_html4 : string

The string contains '<', '>', '"', '&' and the control characters 0-8, 11-12, 14-31, 127.

    val encode : in_enc:Netconversion.encoding ->
           ?out_enc:Netconversion.encoding ->
           ?prefer_name:bool -> ?unsafe_chars:string -> unit -> string -> string

The input string that is encoded as `in_enc` is recoded to `out_enc`, and the following characters are encoded as HTML entity (`&name;` or `&#num;`):

- The ASCII characters contained in `unsafe_chars`
- The characters that cannot be represented in `out_enc`. By default (`out_enc=`Enc_usascii`), only ASCII characters can be represented, and thus all code points >= 128 are encoded as HTML entities. If you pass `out_enc=`Enc_utf8`, all characters can be represented.

For example, the string `"(a<b) & (c>d)"` is encoded as `"(a&lt;b) &amp; (c&gt;d)"`.

It is required that `out_enc` is an ASCII-compatible encoding.

The option `prefer_name` selects whether named entities (e.g. `&lt;`) or numeric entities (e.g. `&#60;`) are prefered.

The efficiency of the function can be improved when the same encoding is applied to several strings. Create a specialized encoding function by passing all arguments up to the unit argument, and apply this function several times. For example:

         let my_enc = encode ~in_enc:`Enc_utf8 () in
         let s1' = my_enc s1 in
         let s2' = my_enc s2 in ...

    type entity_set = [ `Empty | `Html | `Xml ]

    val decode : in_enc:Netconversion.encoding ->
           out_enc:Netconversion.encoding ->
           ?lookup:(string -> string) ->
           ?subst:(int -> string) ->
           ?entity_base:entity_set -> unit -> string -> string

The input string is recoded from `in_enc` to `out_enc`, and HTML entities (`&name;` or `&#num;`) are resolved. The input encoding `in_enc` must be ASCII-compatible.

By default, the function knows all entities defined for HTML 4 (this can be changed using `entity_base`, see below). If other entities occur, the function `lookup` is called and the name of the entity is passed as input string to the function. It is expected that `lookup` returns the value of the entity, and that this value is already encoded as `out_enc`. By default, `lookup` raises a `Failure` exception.

If a character cannot be represented in the output encoding, the function `subst` is called. `subst` must return a substitute string for the character. By default, `subst` raises a `Failure` exception.

The option `entity_base` determines which set of entities are considered as the known entities that can be decoded without help by the `lookup` function: ``Html` selects all entities defined for HTML 4, ``Xml` selects only `&lt;`, `&gt;`, `&amp;`, `&quot;`, and `&apos;`, and ``Empty` selects the empty set (i.e. `lookup` is always called).