Organizing the skins layers

To better understand how the *Skins Tool* and its layers traversal work, I invite you to read the paragraphs about "Using Layers Within a Skin":http://docs.neuroinf.de/PloneBook/ch7.rst#using-layers-within-a-skin and "Managing Skins with the portal_skins Tool":http://docs.neuroinf.de/PloneBook/ch7.rst#managing-skins-with-the-portal-skins-tool in the "chapter 7":http://docs.neuroinf.de/PloneBook/ch7.rst of the official "Plone Book":http://docs.neuroinf.de/PloneBook by Andy McKay. The links are unofficials but they are the only public ones I know that deliver a rendered HTML version of the book, and they are up-to-date. These paragraphs cover TTW Plone customization. Although it is a good way for learning the *Skins Tool* layers traversal mechanism, we know that working in the ZMI is not the best approach when it comes to building a full graphical environment for Plone. When building a skin product on the filesystem, concepts are the same:
The install function first creates a skin selection containing the layers of the skin it is based on, then adds the product specific layers to it. On the filesystem, the product specific layers are the folders that are located in the product 'skins/' directory (*). In practice, if your product is built for customizing a Plone site by adding a few stylesheets and replacing graphical UI elements (images like the logo and some icons), you won't need to have much more than one layer to add to your skin selection (**). But there are situations where it might be useful to have several layers, mainly for organizing skin elements into categories (images, customizations, stylesheets, etc). (*) Any folder located in the 'skins/' directory of your product will be registered as an FSDirectoryView with the portal *Skins Tool*, and then be added to your skin selection layers. Exceptions are folders which name starts with '.' or equals 'CVS' or '{arch}' (This is hardcoded in *Products.DIYPloneStyle.Extensions.utils.getSkinsFolderNames()*). (**) If DIYPloneStyle provides more than one skin layer (if its 'skins/' folder contains more than one folder), it's only for making easier the example removal part of the *Get Started* process.