# HeaderValue class

Representation of a header value in the form:

`value; parameter1=value1; parameter2=value2`

HeaderValue can be used to conveniently build and parse header values on this form.

To build an `accepts` header with the value

    text/plain; q=0.3, text/html

use code like this:

    HttpClientRequest request = ...;
    var v = new HeaderValue("text/plain", {"q": "0.3"});
    request.headers.add(HttpHeaders.acceptHeader, v);
    request.headers.add(HttpHeaders.acceptHeader, "text/html");

To parse the header values use the `parse` static method.

    HttpRequest request = ...;
    List<String> values = request.headers[HttpHeaders.acceptHeader];
    values.forEach((value) {
      HeaderValue v = HeaderValue.parse(value);
      // Use v.value and v.parameters
    });

An instance of HeaderValue is immutable.

Implemented by
  - ContentType

## Constructors

HeaderValue([String value = "", Map<String, String> parameters ])
  Creates a new header value object setting the value and parameters.
  factory

## Properties

parameters → Map<String, String>
  Gets the map of parameters. [...]
  read-only
value → String
  Gets the header value.
  read-only
hashCode → int
  The hash code for this object. [...]
  read-only, inherited
runtimeType → Type
  A representation of the runtime type of the object.
  read-only, inherited

## Methods

toString() → String
  Returns the formatted string representation in the form: [...]
noSuchMethod(Invocation invocation) → dynamic
  Invoked when a non-existent method or property is accessed. [...]
  inherited

## Operators

operator ==(dynamic other) → bool
  The equality operator. [...]
  inherited

## Static Methods

parse(String value, { String parameterSeparator: ";", String valueSeparator: null, bool preserveBackslash: false }) → HeaderValue
  Creates a new header value object from parsing a header value string with both value and optional parameters.