The so called postal acceptance rule has had a long but by no means uneventful history. Its genesis is probably to be found in Adams v Lindsell (1818) 1 B and Ald 681; 106 ER 250 but it was not until Household Fire and Carriage Accident Insurance Co (Ltd) v Grant (1879) 4 Ex D 216 that the rule was itself finally accepted. It had, however, already been applied in Australia: Tooth v Fleming (1859) Legge 1152. Even in quite recent cases in the United States, the rule was still being called "the rule in Adams v Lindsell". But once more firmly established ( Henthorn v Fraser  2 Ch 27), the rule became an important exception to the central principle that acceptance of an offer was not effective until actually communicated to the offeror. Moreover, although the postal system of the late nineteenth century was by all accounts sufficiently reliable and prompt to justify such a gloss on the fundamental principle, the application of the exception was limited to cases in which by reason of general usage or the particular relations between the parties or the terms of the offer itself, the acceptance of an offer by posting was authorised. Further, the letter of acceptance had to be pre paid and properly posted in order to attract the operation of the rule that, in the case in which use of the post was specified or contemplated, acceptance was complete upon posting.
Is the above the same as "explanation of the fundamental principle?"