src/javascript/xhr/XMLHttpRequest.js
function(header) {
				header = header.toLowerCase();

				if (_error_flag || !!~Basic.inArray(header, ['set-cookie', 'set-cookie2'])) {
					return null;
				}

				if (_responseHeaders && _responseHeaders !== '') {
					// if we didn't parse response headers until now, do it and keep for later
					if (!_responseHeadersBag) {
						_responseHeadersBag = {};
						Basic.each(_responseHeaders.split(/\r\n/), function(line) {
							var pair = line.split(/:\s+/);
							if (pair.length === 2) { // last line might be empty, omit
								pair[0] = Basic.trim(pair[0]); // just in case
								_responseHeadersBag[pair[0].toLowerCase()] = { // simply to retain header name in original form
									header: pair[0],
									value: Basic.trim(pair[1])
								};
							}
						});
					}
					if (_responseHeadersBag.hasOwnProperty(header)) {
						return _responseHeadersBag[header].header + ': ' + _responseHeadersBag[header].value;
					}
				}
				return null;
			}
function(header) {
				header = header.toLowerCase();

				if (_error_flag || !!~Basic.inArray(header, ['set-cookie', 'set-cookie2'])) {
					return null;
				}

				if (_responseHeaders && _responseHeaders !== '') {
					// if we didn't parse response headers until now, do it and keep for later
					if (!_responseHeadersBag) {
						_responseHeadersBag = {};
						Basic.each(_responseHeaders.split(/\r\n/), function(line) {
							var pair = line.split(/:\s+/);
							if (pair.length === 2) { // last line might be empty, omit
								pair[0] = Basic.trim(pair[0]); // just in case
								_responseHeadersBag[pair[0].toLowerCase()] = { // simply to retain header name in original form
									header: pair[0],
									value: Basic.trim(pair[1])
								};
							}
						});
					}
					if (_responseHeadersBag.hasOwnProperty(header)) {
						return _responseHeadersBag[header].header + ': ' + _responseHeadersBag[header].value;
					}
				}
				return null;
			}
Returns the header field value from the response of which the field name matches header,
unless the field name is Set-Cookie or Set-Cookie2.

@method getResponseHeader
@param {String} header
@return {String} value(s) for the specified header or null