Document filepath and urlpath launch link parameters in API docs

docs/source/api.rst

@@ -63,6 +63,35 @@ This reports the version of BinderHub and the services it needs to run.
 
 This reports which :doc:`repository providers </reference/repoproviders>` are enabled.
 
+Launch URL Parameters
+---------------------
+
+BinderHub supports special URL parameters to open files or specific Jupyter interfaces directly after launch:
+
+- **filepath**: Opens a specific file or notebook immediately.
+
+  Example:
+
+  .. code-block:: text
+
+     https://mybinder.org/v2/gh/USERNAME/REPO/BRANCH?filepath=notebook.ipynb
+
+- **urlpath**: Opens a specific Jupyter interface.
+
+  Examples:
+
+  - Open JupyterLab with a notebook:
+
+    .. code-block:: text
+
+       ?urlpath=lab/tree/notebook.ipynb
+
+  - Open a terminal directly:
+
+    .. code-block:: text
+
+       ?urlpath=/terminals/1
+
 Events
 ------
 

docs/source/reference/build.rst

@@ -1,17 +1,23 @@
 build
 =====
 
-
 Module: :mod:`binderhub.build`
 ------------------------------
 
 .. automodule:: binderhub.build
 
 .. currentmodule:: binderhub.build
 
-
 :class:`Build`
 --------------
 
 .. autoclass:: Build
     :members:
+
+Additional launch link parameters
+---------------------------------
+
+The following URL parameters are supported when launching a Binder build:
+
+- **filepath**: Path to a specific file in the repository to open automatically.
+- **urlpath**: URL path to open after the Binder server starts. For example, `urlpath=lab` opens JupyterLab.