Add detailed per-topic writeups of relevant areas for python scripts

docs/python_api/in_depth/curevent.rst

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+.. _currentevent:
+
+Current Frame Event
+===================
+
+Aside from information that is immutable or provided across the whole capture, all things in RenderDoc reflect the state snapshotted at a single virtual point - immediately following the execution on the GPU of a single event.
+
+The current event is the :ref:`event ID <eventids>` where this point sits. All things that follow including resource contents like buffers and textures, as well as pipeline state and anything else will be frozen exactly at that point.
+
+Selected vs Current event
+-------------------------
+
+When selecting a marker region that contains many events, there are two distinct concepts:
+
+* The 'selected' event ID is the actual marker region itself, the root event which contains other events and will typically have a lower event ID than its children.
+* The current event ID, or often referred to just as the event ID, is the effective event where the snapshotted state is taken from. When selecting a marker region this effective event is immediately after all child events have happened - so selecting a region surrounding a pass of many draws will show the results of all rendering within that region as if you had selected the very final child event.