Generally, the default context is the top level of your data hierarchy. However, if the request parameter $id is set, the page was accessed via a Permalink, or if an ID is provided in the path to the page, the default context will be set to the item with that ID. Linking with <v:a> automatically generates links in this form. So for example, this code in projects.html would generate links that have the project IDs in their path:
<v:collection path="projects"> <v:a href="/project"><v:text path="name" /></v:a> </v:collection>
So in project.html you can directly access the fields in the project, because the default context is set by the ID in the path:
<v:ctext path="name" />
This will render the name of the Project, even though the context is not explicitly set anywhere. If you want to back out of the default context, simply begin your path expression with a slash, like so:
<v:collection path="/projects"> ... </v:collection>
Because there will be different default contexts on different pages, we generally recommend using a leading slash on all path expressions used in template files.