The final type of Layer is known as the User Layer. This is the layer in which all Layout-specific options, configured via the Customize area, are saved. A layer of this type will automatically be created for the user upon saving their Individual Customizations.
If you wish to make your style publicly viewable, add "layerinfo source_viewable = 1;" to the top of the Layout Layer.
Thanks to jennieknits for pointing out that FAQ #176 is the better FAQ for this. It might be a good idea to have a link to FAQ 176 from FAQ 177 if this happens because while FAQ #176 is the correct place to put this, it's not the place I'd look for it.