diff --git a/doc/conf.py b/doc/conf.py
index 2864fed2d..2a9865f5c 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -40,10 +40,13 @@
     "--InlineBackend.figure_formats={'svg', 'pdf'}",
     "--InlineBackend.rc=figure.dpi=96",
 ]
-# nbsphinx_execute = "never"  # uncomment this to speed up doc build
+# use FAST=1 to speed up doc build
+if bool(os.environ.get("FAST", False)):
+    nbsphinx_execute = "never"
 
 autoclass_content = "both"
 autosummary_generate = True
+autodoc_member_order = "groupwise"
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
diff --git a/doc/reference.rst b/doc/reference.rst
index 7f18db645..21aef73b9 100644
--- a/doc/reference.rst
+++ b/doc/reference.rst
@@ -46,9 +46,15 @@ Cost functions
 
 .. automodule:: iminuit.cost
     :members:
+    :inherited-members:
 
 Utilities
 ---------
 
 .. automodule:: iminuit.util
+    :exclude-members: Matrix
+    :inherited-members:
+
+.. autoclass:: iminuit.util.Matrix
     :members:
+    :no-inherited-members:
diff --git a/src/iminuit/cost.py b/src/iminuit/cost.py
index 0ad2b7ff4..7d82321fe 100644
--- a/src/iminuit/cost.py
+++ b/src/iminuit/cost.py
@@ -103,6 +103,8 @@ class BohmZechTransform:
     Apply Bohm-Zech transform.
 
     See Bohm and Zech, NIMA 748 (2014) 1-6.
+
+    :meta private:
     """
 
     def __init__(self, val: _ArrayLike, var: _ArrayLike):
@@ -455,13 +457,21 @@ def _soft_l1_cost(y, ye, ym):
 
 
 class Cost(abc.ABC):
-    """Base class for all cost functions."""
+    """
+    Base class for all cost functions.
+
+    :meta private:
+    """
 
     __slots__ = ("_func_code", "_verbose")
 
     @property
     def errordef(self):
-        """For internal use."""
+        """
+        For internal use.
+
+        :meta private:
+        """
         return self._errordef()
 
     def _errordef(self):
@@ -469,7 +479,11 @@ def _errordef(self):
 
     @property
     def func_code(self):
-        """For internal use."""
+        """
+        For internal use.
+
+        :meta private:
+        """
         return self._func_code
 
     @property
@@ -681,7 +695,11 @@ def visualize(
 
 
 class MaskedCost(Cost):
-    """Base class for cost functions that support data masking."""
+    """
+    Base class for cost functions that support data masking.
+
+    :meta private:
+    """
 
     __slots__ = "_data", "_mask", "_masked"
 
@@ -721,7 +739,11 @@ def _update_cache(self):
 
 
 class UnbinnedCost(MaskedCost):
-    """Base class for unbinned cost functions."""
+    """
+    Base class for unbinned cost functions.
+
+    :meta private:
+    """
 
     __slots__ = "_model", "_log"
 
@@ -928,7 +950,11 @@ def _call(self, args):
 
 
 class BinnedCost(MaskedCost):
-    """Base class for binned cost functions."""
+    """
+    Base class for binned cost functions.
+
+    :meta private:
+    """
 
     __slots__ = "_xe", "_ndim", "_bztrafo"
 
@@ -1011,7 +1037,11 @@ def _pred(self, args: _tp.Sequence[float]) -> np.ndarray:
 
 
 class BinnedCostWithModel(BinnedCost):
-    """Base class for binned cost functions."""
+    """
+    Base class for binned cost functions with parametric model.
+
+    :meta private:
+    """
 
     __slots__ = "_xe_shape", "_model", "_model_arg"
 
diff --git a/src/iminuit/util.py b/src/iminuit/util.py
index 5f8d601a2..25c9a1007 100644
--- a/src/iminuit/util.py
+++ b/src/iminuit/util.py
@@ -36,6 +36,8 @@ class BasicView(abc.ABC):
 
     Derived classes need to implement methods _set and _get to access
     specific properties of the parameter state.
+
+    :meta private:
     """
 
     __slots__ = ("_minuit", "_ndim")