As you are no doubt aware the Theravada monastic world is divided into Nikaya - sects and sub-sects.
In Thailand there are 2 Nikaya (and many subgroups which are not strictly speaking sub-nikaya).
The Sangha in Burma is divided into 9 Nikaya.
Sri Lanka has 3 main Nikaya, but these are split into more than 30 sub-nikaya.
Cambodia and Laos 2 I believe.
Generally monks from one nikaya will not perform legal kamma (such as ordinations) with monks of another nikaya.
However, there is a ceremony known as Dalhikamma which has been called a 'strengthening procedure'. Visiting monks from other nikaya can participate in Dalhikamma and thereby have their original ordination recognised without the need to re-ordain.
I would like to learn of the origin and textual basis for 'Dalhikamma' and also hear about contemporary applications of it in Theravada lands.
Does anyone know more?