When you first install SharePoint Foundation, a file named WEBTEMP.XML identifies each site definition, where Temp in this context means template, not temporary. It contains information pertaining to the site definitions and configurations for the site definition. It also determines how the site appears to users who are creating new sites. You can find this file at Program FilesCommon FilesMicrosoft Sharedweb server extensions14TEMPLATE1033XML, where 1033 is the current locale ID. A shortened version of this file is as follows:

<?xml version="1.0" encoding="utf-8"?>
<!-- _lcid="1033" _version="14.0.4762" _dal="1" -->
<!-- _LocalBinding -->
<Templates xmlns:ows="Microsoft SharePoint">
  <Template Name="GLOBAL" SetupPath="global" ID="0">
    <Configuration ID="0" Title="Global template" Hidden="TRUE" ImageUrl=""
      Description="This template is used for initializing a new site." >
    </Configuration>
   </Template>
  <Template Name="STS" ID="1">
    <Configuration ID="0" Title="Team Site" Hidden="FALSE"
      ImageUrl="/_layouts/images/stts.png"
      Description="A site for teams to quickly organize, author, and share
        information. It provides a document library, and lists for managing
        announcements, calendar items, tasks, and discussions."
      DisplayCategory="Collaboration" >
    </Configuration>
    <Configuration ID="1" Title="Blank Site" Hidden="FALSE"
      ImageUrl="/_layouts/images/stbs.png"
      Description="A blank site for you to customize based on your requirements."
      DisplayCategory="Collaboration" AllowGlobalFeatureAssociations="False" >
    </Configuration>
    <Configuration ID="2" Title="Document Workspace" Hidden="FALSE"
      ImageUrl="/_layouts/images/stdw.png"
      Description="A site for colleagues to work together on a document. It
        provides a document library for storing the primary document and supporting
        files, a tasks list for assigning to-do items, and a links list for resources
        related to the document."
      DisplayCategory="Collaboration" >
    </Configuration>
  </Template>
. . .
</Templates>

Each <Template></Template> block identifies a set of similar site definitions. Each <Template> tag contains:

Within each <Template></Template> block, there’s one <configuration> tag for each site definition, which contains:

Further information about each site definition appears in a file named ONET.XML. Because the WEBTEMP.XML file specified several template names (STS, MPS, Blog, Wiki, Central Administration), there are more than one ONET.XML files. To find these files, first browse to Program FilesCommon FilesMicrosoft SharedWeb server extensions14TEMPLATESiteTemplates, and then go to the following locations:

Each ONET.XML file defines a series of common elements for individual sites to use. These include the following:

Several types of tasks can be performed in ONET.XML to customize a site definition:

SharePoint Foundation includes the global site definition file, which you can find at Program FilesCommon FilesMicrosoft Sharedweb server extensions14TEMPLATEGLOBALXMLONET.XML. This file contains provisioning information that can be used by every site definition such as base types, base master page, and so on. This file alleviates redundant data from being inserted into each ONET.XML file for each site definition. The following code snippet shows the base structure and elements that are included in the ONET.XML file:

<?xml version="1.0" encoding="utf-8"?>
<Project Title="Site Definition" Revision="1" ListDir=""
      xmlns:ows="Microsoft SharePoint">
   <NavBars/>
   <ListTemplates/>
   <DocumentTemplates/>
   <BaseTypes/>
   <Configurations>
...
      <Configuration ID="0" Name="Default">
         <Lists/>
         <Modules>
            <Module Name="Default" />
         </Modules>
         <SiteFeatures>
            <!-- BasicWebParts Feature -->
            <Feature ID="00BFEA71-1C5E-4A24-B310-BA51C3EB7A57" />
...
         </SiteFeatures>
         <WebFeatures>
            <!-TeamCollab Feature -->
            <Feature ID="00BFEA71-4EA5-48D4-A4AD-7EA5C011ABE5" />
...
         </WebFeatures>
      </Configuration>
...
   </Configurations>
   <Modules>
      <Module Name="Default" Url="" Path="">
         <File Url="default.aspx" NavBarHome="True" />
      </Module>
...
   </Modules>
   <Components>
      <FileDialogPostProcessor ID="BDEADEE4-C265-11d0-BCED-00A0C90AB50F" />
   </Components>
   <ServerEmailFooter>$Resources:ServerEmailFooter;</ServerEmailFooter>
</Project>

NavBars defines the top and side navigation bar. This node can contain additional NavBar elements, and the links can be added by using NavBarLink elements.

The ListTemplates section specifies the list definitions that are part of a site definition. The ListTemplate element also specifies a display name for the list definition and whether the option to add a link on the Quick Launch appears selected by default on the new page.

In addition, this element specifies the description of the list definition and the path to the image representing the list definition, which are both displayed on the Create page. This element is supported in SharePoint Foundation 2010 only for backward compatibility. If a list type needs to be defined, it needs to be defined as a Feature.

The DocumentTemplates elements describe what document templates will be used in document libraries.

The BaseTypes element of the global ONET.XML file is used during site or list creation to define the basic list types on which all list definitions in SharePoint Foundation are based. Each list template that is specified in the list templates section is identified with one of the base types: Generic List, Document Library, Discussion Forum, Vote or Survey, or Issues List. It is important to note that the BaseTypes section can only be implemented in the Global.XML file.

The Configurations element contains one or more configuration elements that contain the lists, modules, and Features that are created when the site definition is used to create a site.

The Components element specifies components to include in sites created through the definition.

The ServerEmailFooter element is used to determine the footer used in email sent from the server.

Making changes to the default WEBTEMP.XML and ONET.XML files that come with Share-Point Foundation is not a best practice. The two main reasons are:

Therefore, an incorrect change, even if it works for new sites, could break hundreds or thousands of existing sites. Thus, the correct approach is to create new site definitions rather than change existing ones.

You can utilize Visual Studio to create a new site definition and package the site definition, which you can then deliver to a client. To create a site definition, use Visual Studio to create a Site Definition project, which automatically generates an ONET.XML, WEBTEMP*.XML, and default.aspx files. These files can be modified to include the configuration needed for your custom site definition. You can deploy the Site Definition project to your debug site and test your solution.

If there is a site definition that already exists from the out-of-the-box site definitions that closely resembles your needed solution, you can use a copy of those files as a template from which to create your custom site definition. This will save time as you will not need to create the entire solution from scratch.

When working with site definitions, you might want to add an additional Feature to a site definition, but don’t want to modify the site definition files themselves. This is sometimes the case when you want to extend the functionality of an out-of-the-box site definition in SharePoint. This can be accomplished by utilizing a concept called Feature Stapling.

Feature stapling is accomplished by creating a new Feature that references one or more existing site definitions by utilizing a FeatureSiteTemplateAssociation element. This element defines the association between the new feature and existing site definitions so that the associated Features will be automatically activated.

One of the new improvements to SharePoint 2010 that makes the stapling process easier is the implementation of new out-of-the-box event receivers. The event receivers that are beneficial to Feature Stapling are the web events that capture when a site is being provisioned and when a site has been provisioned.

A good example of how these events can be used is when you need to manipulate a list that is associated with a site definition after a site is provisioned. Previously, developers would use the FeatureActivated event and place some type of custom check and delay the activation process to make sure that any changes to the list occurred once the entire site was provisioned. This was required because by default the FeatureActivated event would fire before the list you needed to manipulate was created. If you did not provide the custom check, in many instances a System.Argument exception occurred, letting you know that list did not exist. Now with SharePoint 2010, you can accurately capture events after a site has been provisioned and then make the needed changes to the list without delaying the activation process.