title: urlresolver
---
type: method
---
summary: Registers a custom URL resolver function.
---
body:

This is very experimental API and used to register a custom URL resolver
function with the environment.  It's invoked whenever a node has matched but
more data is left to parse.  This can be used to implement virtual items.
This works in combination with [generator :ref](../generator/) but handles the
URL matching part of the equation.

The registered function is invoked with a source object and a list of
URL path segments.

## Example

```python
from lektor.sourceobj import VirtualSourceObject
from lektor.utils import build_url

class Source(VirtualSourceObject):

    @property
    def path(self):
        return self.record.path + '@source'

    @property
    def url_path(self):
        return build_url([self.record.url_path, 'source.txt'])

@env.urlresolver
def match_source_file(node, url_path):
    if url_path == ['source.txt'] \
       and isinstance(node, Record) \
       and not node.is_attachment:
        return Source(node)
```