Supplement documentation regarding UI default style file.

Docs/Reference.dox

@@ -1349,7 +1349,7 @@ User interface elements derive from Serializable, so they can be serialized to/f
 
 The function \ref UI::LoadLayout "LoadLayout()" in UI will take an XML file and instantiate the elements defined in it. To be valid XML, there should be one root-level %UI element. An optional style XML file can be specified; the idea is to first read the element's style from that file, then fill in the rest from the actual layout XML file. This way the layout file can be relatively simple, as the majority of the data is already defined.
 
-Note that a style can not be easily applied recursively to the loaded elements afterward. Therefore remember to specify the style file already when loading, or alternatively \ref UIElement::SetDefaultStyle "assign a default style file" to the %UI root element, which will then be picked up by all loaded layouts.
+Note that a style can not be easily applied recursively to the loaded elements afterward. Therefore remember to specify the style file already when loading, or alternatively \ref UIElement::SetDefaultStyle "assign a default style file" to the %UI root element, which will then be picked up by all loaded layouts. This works because the %UI subsystem searches the style file by going up the parental chain starting from target parent %UI element. The search stops immediately when a style file is found or when it has reached the root element. Also note that Urho3D does not limit the number of style files being used at the same time in an application. You may have different style file set along the %UI parental hierarchy, if your application needs that.
 
 See the elements' C++ code for all supported attributes, and look at the editor's user interface layouts in the Bin/Data/UI directory for examples. You can also use the Editor application to create %UI layouts. The serialization format is similar to scene XML serialization, with three important differences: