Better document branch priorities.

docs/source/codedoc.rst

@@ -338,41 +338,48 @@ Branch priorities
 -----------------
 
 When pydoctor deals with try/except/else or if/else block, it makes sure that the names defined in 
-the "principal" flow do not get overridden by names defined in the except handlers or ifs' else block. 
-New names defined in these block will be processed normally.
+the main flow has precedence over the definitions in ``except`` handlers or ``else`` blocks.
 
 Meaning that in the context of the code below, ``ssl`` would resolve to ``twisted.internet.ssl``:
 
 .. code:: python
 
     try:
+        # main flow
         from twisted.internet import ssl as _ssl
     except ImportError:
-        ssl = None
+        # exceptional flow
+        ssl = None # ignored since 'ssl' is defined in the main flow below.
+        var = True # not ignored since 'var' is not defined anywhere else.
     else:
+        # main flow
         ssl = _ssl
 
-Similarly, in the context of the code below, the first ``CapSys`` class will be 
-documented and the second one will be ignored.
+Similarly, in the context of the code below, the ``CapSys`` protocol under the ``TYPE_CHECKING`` block will be 
+documented and the runtime version will be ignored.
 
 .. code:: python
 
     from typing import TYPE_CHECKING
     if TYPE_CHECKING:
+        # main flow
         from typing import Protocol
         class CapSys(Protocol):
             def readouterr() -> Any:
                 ...
     else:
-        class CapSys(object): # ignored
+        # secondary flow
+        class CapSys(object): # ignored since 'CapSys' is defined in the main flow above.
             ...
 
-.. But sometimes pydoctor can be better off analysing the ``TYPE_CHECKING`` blocks and should 
-.. stick to the runtime version of the code instead. 
-
-.. You can instruct pydoctor do to such things with a custom system class. 
-
-.. .. code:: python
-
-..     class MySystem(model.System):
-..         eval_if = {'my_mod':{'TYPE_CHECKING':False}}
+But sometimes pydoctor can be better off analysing the ``TYPE_CHECKING`` blocks and should 
+stick to the runtime version of the code instead. 
+For these case, you might want to inverse the condition of if statement: 
+
+ .. code:: python
+    if not TYPE_CHECKING:
+        # main flow
+        from ._implementation import Thing
+    else:
+        # secondary flow
+        from ._typing import Thing # ignored since 'Thing' is defined in the main flow above.