This addon implements a
subdivision scheme called deathguppie.
It is ideal for creating more detail locally when sculpting.
Documentation
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 (2.79: button in
the Mesh Tool panel, 2.80: tab in N-panel at right of 3D View).
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).