A function to be called to transform from_value to to_value.
If this is the transform_to function of a binding, then from_value
is the source_property on the source object, and to_value is the
target_property on the target object. If this is the
transform_from function of a %G_BINDING_BIDIRECTIONAL binding,
then those roles are reversed.
A function to be called to transform
from_valuetoto_value.If this is the
transform_tofunction of a binding, thenfrom_valueis thesource_propertyon thesourceobject, andto_valueis thetarget_propertyon thetargetobject. If this is thetransform_fromfunction of a %G_BINDING_BIDIRECTIONAL binding, then those roles are reversed.