[HACKERS] define type_transform to new user defined type

[Mohsen SM]

 I want to create new type that is similar to varchar.
its size is variable.
I use CREATE TYPE query.
I define for that type this functions:
1-typein
2-typeoute
3-typemodify_input
4-typemodify_output
5-type_transform
I can define 1 to 4 functions in CREATE TYPE
but I can't define type_transform for that type. how did I can define
type_transform for that type?