API Provide a thin alternative to loadPanel/submitForm.

This is needed in some situations when we only want to update a
small single component, sometimes even using a different controller to
the one implied in the URL.

An example here is reloading dynamically the subsite dropdown without
reloading the entire page, updating a filter sidebar or suchlike.

admin/javascript/LeftAndMain.js

@@ -115,7 +115,15 @@ jQuery.noConflict();
 		 */
 		$('.cms-container').entwine({
 
-			CurrentXHR: null,
+			/**
+			 * Tracks current panel request.
+			 */
+			StateChangeXHR: null,
+
+			/**
+			 * Tracks current fragment-only parallel PJAX requests.
+			 */
+			FragmentXHR: {},
 
 			StateChangeCount: 0,
 
@@ -419,7 +427,7 @@ jQuery.noConflict();
 			 */
 			handleStateChange: function() {
 				// Don't allow parallel loading to avoid edge cases
-				if(this.getCurrentXHR()) this.getCurrentXHR().abort();
+				if(this.getStateChangeXHR()) this.getStateChangeXHR().abort();
 
 				var self = this, h = window.History, state = h.getState(),
 					fragments = state.data.pjax || 'Content', headers = {},
@@ -455,7 +463,7 @@ jQuery.noConflict();
 					headers: headers,
 					url: state.url,
 					complete: function() {
-						self.setCurrentXHR(null);
+						self.setStateChangeXHR(null);
 						// Remove loading indication from old content els (regardless of which are replaced)
 						contentEls.removeClass('loading');
 					},
@@ -465,7 +473,75 @@ jQuery.noConflict();
 					}
 				});
 
-				this.setCurrentXHR(xhr);
+				this.setStateChangeXHR(xhr);
+			},
+
+			/**
+			 * ALternative to loadPanel/submitForm.
+			 *
+			 * Triggers a parallel-fetch of a PJAX fragment, which is a separate request to the
+			 * state change requests. There could be any amount of these fetches going on in the background,
+			 * and they don't register as a HTML5 history states.
+			 *
+			 * This is meant for updating a PJAX areas that are not complete panel/form reloads. These you'd
+			 * normally do via submitForm or loadPanel which have a lot of automation built in.
+			 *
+			 * On receiving successful response, the framework will update the element tagged with appropriate
+			 * data-pjax-fragment attribute (e.g. data-pjax-fragment="<pjax-fragment-name>"). Make sure this element
+			 * is available.
+			 *
+			 * Example usage:
+			 * $('.cms-container').loadFragment('admin/foobar/', 'FragmentName');
+			 *
+			 * @param url string Relative or absolute url of the controller.
+			 * @param pjaxFragments string PJAX fragment(s), comma separated.
+			 */
+			loadFragment: function(url, pjaxFragments) {
+
+				var self = this,
+					xhr,
+					headers = {},
+					baseUrl = $('base').attr('href'),
+					fragmentXHR = this.getFragmentXHR();
+
+				// Make sure only one XHR for a specific fragment is currently in progress.
+				if(
+					typeof fragmentXHR[pjaxFragments]!=='undefined' &&
+					fragmentXHR[pjaxFragments]!==null
+				) {
+					fragmentXHR[pjaxFragments].abort();
+					fragmentXHR[pjaxFragments] = null;
+				}
+
+				url = $.path.isAbsoluteUrl(url) ? url : $.path.makeUrlAbsolute(url, baseUrl);
+				headers['X-Pjax'] = pjaxFragments;
+
+				xhr = $.ajax({
+					headers: headers,
+					url: url,
+					success: function(data, status, xhr) {
+						var elements = self.handleAjaxResponse(data, status, xhr, null);
+
+						// We are fully done now, make it possible for others to hook in here.
+						self.trigger('afterloadfragment', { data: data, status: status, xhr: xhr, elements: elements });
+					},
+					error: function(xhr, status, error) {
+						self.trigger('loadfragmenterror', { xhr: xhr, status: status, error: error });
+					},
+					complete: function() {
+						// Reset the current XHR in tracking object.
+						var fragmentXHR = self.getFragmentXHR();
+						if(
+							typeof fragmentXHR[pjaxFragments]!=='undefined' &&
+							fragmentXHR[pjaxFragments]!==null
+						) {
+							fragmentXHR[pjaxFragments] = null;
+						}
+					}
+				});
+
+				// Store the fragment request so we can abort later, should we get a duplicate request.
+				fragmentXHR[pjaxFragments] = xhr;
 			},
 
 			/**

docs/en/reference/cms-architecture.md

@@ -287,6 +287,47 @@ tracked in the browser history, use the `pjax` attribute on the state data.
 
 	$('.cms-container').loadPanel('admin/pages', null, {pjax: 'Content'});
 
+## Loading lightweight PJAX fragments
+
+Normal navigation between URLs in the admin section of the Framework occurs through `loadPanel` and `submitForm`.
+These calls make sure the HTML5 history is updated correctly and back and forward buttons work. They also take
+care of some automation, for example restoring currently selected tabs.
+
+However there are situations when you would like to only update a small area in the CMS, and when this operation should
+not trigger a browser's history pushState. A good example here is reloading a dropdown that relies on backend session
+information that could have been updated as part of action elsewhere, updates to sidebar status, or other areas
+unrelated to the main flow.
+
+In this case you can use the `loadFragment` call supplied by `LeftAndMain.js`. You can trigger as many of these in
+parallel as you want. This will not disturb the main navigation.
+
+		$('.cms-container').loadFragment('admin/foobar/', 'Fragment1');
+		$('.cms-container').loadFragment('admin/foobar/', 'Fragment2');
+		$('.cms-container').loadFragment('admin/foobar/', 'Fragment3');
+
+The ongoing requests are tracked by the PJAX fragment name (Fragment1, 2, and 3 above) - resubmission will
+result in the prior request for this fragment to be aborted. Other parallel requests will continue undisturbed.
+
+You can also load multiple fragments in one request, as long as they are to the same controller (i.e. URL):
+
+		$('.cms-container').loadFragment('admin/foobar/', 'Fragment2,Fragment3');
+
+This counts as a separate request type from the perspective of the request tracking, so will not abort the singular
+`Fragment2` nor `Fragment3`.
+
+Upon the receipt of the response, the fragment will be injected into DOM where a matching `data-pjax-fragment` attribute
+has been found on an element (this element will get completely replaced). Afterwards a `afterloadfragment` event
+will be triggered. In case of a request error a `loadfragmenterror` will be raised and DOM will not be touched.
+
+You can hook up a response handler that obtains all the details of the XHR request like this:
+
+		'from .cms-container': {
+			onafterloadfragment: function(e, data) {
+				// Say 'success'!
+				alert(data.status);
+			}
+		}
+
 ## Ajax Redirects
 
 Sometimes, a server response represents a new URL state, e.g. when submitting an "add record" form,