"Receptio in complexu": from the Codex Justinianus and Roman Law to Germany and Indonesia

I am still working on an entry on L.W.C. van den Berg for CMR, the Bibliographical History of Christian Muslim Relations. Yesterday I read an interesting reference to his best known theory: of Receptio in Complexu. This is the reception of the full content of Islamic Law at the moment of conversion to Islam. I was reading a second article on 'Deviations from Muslim Personal Law in Indonesia, esp. Java and Madura' with the title Nalezing, in BKI, Bijdragen tot de taal-, land-, en volkenkunde, 45 (1895), 291-314. Among other topics Van den Berg here gives the example of  the requirements for a valid marriage: a 'priest' (penghulu or naib) is traditionally requiredfor the validity, although orthodox and 'pure' Muslim Law only requires the two witnesses, the bridegroom and the wali or representatives of the bride.
Then Van den Berg turns to the more theoretical questions of the reception of Muslim Law in Indoensia. He gives two arguments. First is the shahada: the two lines of the confession of faith are both important: there is One God, Muhammad is his Prophet. The second line must be understood as acceptance of the full shari'a, at least in general theory. This is also shown in the image of the double sword of Muhammad in the Muharrar of Sinusi (not Sanusi, but Van den Berg writes Sinoesi).

Here Van den Berg sees the great difference between Islam and Christianity: the latter only defines the general rules of ethical conduct and leaves it to the local communities to define more precise rulings, while Islam is poor in the general rules of conduct and has much more detailed about human conduct. In a reation on his first article on family law (and its many deviations in Java and Madura) one esteemed colleague wrote: 'Is it not possbile to become a selective Muslim, accepting only some rulings of Islam, while neglecting other aspects?' One Mr. M.C. Piepers had written: 'men kan toch ook een godsdienst voor een deel aannemen’  [it is possible to accept a religion partly']. This is not possible for L.W.C. van den Berg because in this condition the second section of the shahada is neglected.

Then, on pages 310-312 twice the terminology of receptio in complexu is used (for the first time as I know). Van den Berg has taken it from a debate in Germany about the spread of Roman Law in the Middle Ages in Germany. He refers to a book in German byWindscheid, Lehrbuch des Pandektenrechts, dl I Par. 2; also to W. Modderman, De receptie van het Romeinsche Recht p. 14, 23, 47 en 53 en vv.  The book by Modderman is from 1874. 

Not all details of Roman Law were practised in mediaeval Europe, but still with the acceptance of Christianity also the 'Christian Law' or Roman Law was accepted in that time. It remains unclear to me how Van den Berg interprets his 'deviations': he does not like adat law because it is not precise and does not give certainty in society. And what about non-Muslim rulers who have authority over Muslims: should they apply adat law or Muslim Law? So far, the reception in complexu has become more a problem for me than it was before!