This addon implements a
subdivision scheme called deathguppie.
It is ideal for creating more detail locally when sculpting.
First go to User Preferences->Addons and enable the DeathGuppie addon in
the Mesh category.
Go to EditMode, select some elements and invoke the addon (button in the
Mesh Tool panel).
The selected area will be subdivided according to the deathguppie algorithm.
Subdivision is destructive so this is no modifier but a mesh operation.
Selected area after operation allows for further sudividing the area.
The smooth tickbox chooses between smooth and non-smooth subdivision.
The Select inner only tickbox sets what is left selected after operation,
only inner faces or everything.
BEWARE - deathguppie will only subdivide grids of quads!
If you wish to hotkey DeathGuppie:
In the Input section of User Preferences at the bottom of the 3D View >
Mesh section click 'Add New' button.
In the Operator Identifier box put 'mesh.deathguppie'.
Assign a hotkey.
Save as Default (Optional).