First batch of signature documentation changes; using default argument syntax where applicable.
diff --git a/Doc/library/abc.rst b/Doc/library/abc.rst
index 42f508d..31bd896 100644
--- a/Doc/library/abc.rst
+++ b/Doc/library/abc.rst
@@ -158,7 +158,7 @@
       multiple-inheritance.
 
 
-.. function:: abstractproperty(fget[, fset[, fdel[, doc]]])
+.. function:: abstractproperty(fget=None, fset=None, fdel=None, doc=None)
 
    A subclass of the built-in :func:`property`, indicating an abstract property.