The `text-streams` module provides streams for reading and writing text using particular character encodings. @class @constructor Creates a buffered input stream that reads text from a backing stream using a given text encoding. @param inputStream {stream} The backing stream, an [`nsIInputStream`](http://mxr.mozilla.org/mozilla-central/source/xpcom/io/nsIInputStream.idl). It must already be opened. @param [charset] {string} `inputStream` is expected to be in the character encoding named by this value. If not specified, "UTF-8" is assumed. See [`nsICharsetConverterManager.idl`](http://mxr.mozilla.org/mozilla-central/source/intl/uconv/idl/nsICharsetConverterManager.idl) for documentation on how to determine other valid values for this. @property {boolean} True if the stream is closed. @method Closes both the stream and its backing stream. @method Reads and returns a string from the stream. If the stream is closed, an exception is thrown. @param [numChars] {number} The number of characters to read. If not given, the remainder of the stream is read. @returns {string} The string read. If the stream is at the end, the empty string is returned. @class @constructor Creates a buffered output stream that writes text to a backing stream using a given text encoding. @param outputStream {stream} The backing stream, an [`nsIOutputStream`](http://mxr.mozilla.org/mozilla-central/source/xpcom/io/nsIOutputStream.idl). It must already be opened. @param [charset] {string} Text will be written to `outputStream` using the character encoding named by this value. If not specified, "UTF-8" is assumed. See [`nsICharsetConverterManager.idl`](http://mxr.mozilla.org/mozilla-central/source/intl/uconv/idl/nsICharsetConverterManager.idl) for documentation on how to determine other valid values for this. @property {boolean} True if the stream is closed. @method Flushes the backing stream's buffer and closes both the stream and the backing stream. If the stream is already closed, an exception is thrown. @method Flushes the backing stream's buffer. @method Writes a string to the stream. If the stream is closed, an exception is thrown. @param str {string} The string to write. @method Writes a string on a background thread. After the write completes, the backing stream's buffer is flushed, and both the stream and the backing stream are closed, also on the background thread. If the stream is already closed, an exception is thrown immediately. @param str {string} The string to write. @param [callback] {callback} *`callback`*, if given, must be a function. It's called as `callback(error)` when the write completes. `error` is an `Error` object or undefined if there was no error. Inside *`callback`*, `this` is the `TextWriter` object.