Use the docstring instead of a rst entry

no need to edit the doc generation script actually

renpy/exports.py

@@ -102,7 +102,7 @@ from renpy.character import show_display_say, predict_show_display_say, display_
 import renpy.audio.sound as sound
 import renpy.audio.music as music
 
-from renpy.statements import register as register_statement
+from renpy.statements import register as register_statement, register_decorator
 from renpy.text.extras import check_text_tags
 
 from renpy.memory import profile_memory, diff_memory, profile_rollback

renpy/statements.py

@@ -309,6 +309,65 @@ def register(
 
     parsers.add(name, parse_data)
 
+# import inspect # only works in py3
+# register_params = frozenset(inspect.signature(register).parameters) - {"name", "parse", "execute"}
+register_params = frozenset((
+    # "name", # special-cased
+    # "parse", # special-cased
+    "lint",
+    # "execute", # special-cased
+    "predict",
+    "next",
+    "scry",
+    "block",
+    "init",
+    "translatable",
+    "execute_init",
+    "init_priority",
+    "label",
+    "warp",
+    "translation_strings",
+    "force_begin_rollback",
+    "post_execute",
+    "post_label",
+    "predict_all",
+    "predict_next",
+    "execute_default",
+    "reachable",
+))
+def register_decorator(cls):
+    """
+    :doc: statement_register decorator
+    :args:
+
+    A class decorator which registers a new statement.
+
+    The name of the statement will be the class name unless a ``name``
+    class attribute is present, which should be a string.
+
+    The `parse` parameter to :func:`renpy.register_statement` should
+    either be the class constructor itself, or a method named ``parse``
+    (likely a class method or static method) returning an instance of
+    the class.
+
+    For the `execute` parameter, Ren'Py will look for a method named
+    ``execute`` on the class, or if it is not found, will use the class's
+    ``__call__`` method to call like a function the object created by `parse`.
+
+    All other parameters to :func:`renpy.register_statement` should be set as
+    class attributes or methods with the same name.
+    """
+    name = getattr(cls, "name", cls.__name__)
+    parse = getattr(cls, "parse", cls)
+    execute = getattr(cls, "execute", None) or cls.__call__
+    register(
+        name,
+        parse=parse,
+        execute=execute,
+        **{k:getattr(cls, k) for k in register_params.intersection(vars(cls))}
+    )
+    return cls
+
 
 def parse(node, line, subblock):
     """