This enables you to edit the active texture.
The mapping (i.e. the type of projection) is taken into account.
The grid lines are drawn according to the type of projection chosen, e.g., spherical mapping is shown with a spherical grid. An exception is UVW mapping. Here the grid is displayed over the entire viewport.
The texture axes of the object are shown with an envelope on whose surface the texture can be moved and rotated by using the Move, Scale and Rotate tools.
A left/right drag of the mouse will move the texture along its X axis, an up/down drag will move it along its Y axis. The Scale function uses the same principle, only here the texture does not get moved but re-sized.