src/javascript/xhr/XMLHttpRequest.js
function(mime) {
				var matches, charset;

				// 1
				if (!!~Basic.inArray(_p('readyState'), [XMLHttpRequest.LOADING, XMLHttpRequest.DONE])) {
					throw new x.DOMException(x.DOMException.INVALID_STATE_ERR);
				}

				// 2
				mime = Basic.trim(mime.toLowerCase());

				if (/;/.test(mime) && (matches = mime.match(/^([^;]+)(?:;\scharset\=)?(.*)$/))) {
					mime = matches[1];
					if (matches[2]) {
						charset = matches[2];
					}
				}

				if (!Mime.mimes[mime]) {
					throw new x.DOMException(x.DOMException.SYNTAX_ERR);
				}

				// 3-4
				_finalMime = mime;
				_finalCharset = charset;
			}
function(mime) {
				var matches, charset;

				// 1
				if (!!~Basic.inArray(_p('readyState'), [XMLHttpRequest.LOADING, XMLHttpRequest.DONE])) {
					throw new x.DOMException(x.DOMException.INVALID_STATE_ERR);
				}

				// 2
				mime = Basic.trim(mime.toLowerCase());

				if (/;/.test(mime) && (matches = mime.match(/^([^;]+)(?:;\scharset\=)?(.*)$/))) {
					mime = matches[1];
					if (matches[2]) {
						charset = matches[2];
					}
				}

				if (!Mime.mimes[mime]) {
					throw new x.DOMException(x.DOMException.SYNTAX_ERR);
				}

				// 3-4
				_finalMime = mime;
				_finalCharset = charset;
			}
Sets the Content-Type header for the response to mime.
Throws an "InvalidStateError" exception if the state is LOADING or DONE.
Throws a "SyntaxError" exception if mime is not a valid media type.

@method overrideMimeType
@param String mime Mime type to set