Code Snippets In SharePoint Designer 2010
Code snippets are pre-defined blocks of code (or html source if you so prefer). You can use a snippet to enter a short block quickly and easily – just as you do in Visual Studio, for example.
In SharePoint Designer, while in source mode (the code view), press CTRL+ENTER and you will see a list of possible snippets together with a link to customize the list. The link is handy as the snippets themselves are not easy to find: from File, go to Options – to get the SharePoint Designer options dialog. From General, select Page Editor Options and then select the Code Snippets tab. You can see the available ones with their content, add new, modify existing or remove.
While at this screen, it is worth inspecting all the available options and settings on otehr tabs and other configurations like application options, ribbon and quick access toolbar.
For the current site open in Designer, there is also a site options link specific to current site (the Site tab on the ribbon).