x1 (digit string/byte, storage system, convention) has endianness x2 ("ce'o" sequence of numbers (li); description (ka?)); x1 is x2-endian.
For filling x2 with a "ce'o" sequence, the following convention is used: 1 (li pa) represents the most important/significant term in the actual number and the significance of the term is inversely proportional with the size of the number representing it in the sequence; the sequence will be as short as possible, will have no blank spaces, and each term in it will be a positive integer such that, if there are at least two terms, for any term, there exists another term which differs from it by 1; the placement of a term in the sequence indicates the location of a generic term in an actual number with the signficance which is represented by it, in the given base. For example, "li pa ce'o li re" means "big-endian" (the most significant term (represented by "li pa") comes first in the sequence and the sequence has exactly two terms), "li re ce'o li pa" means "little-endian" ((the most significant term (represented by "li pa") comes last in the sequence and the sequence has exactly two terms), "li re ce'o li ci ce'o le pa" is middle-endian (as in the conventional representation of dates in the U.S. (MM-DD-YYYY); the second most signifant term (represented by "li re"; example: month) comes first, the least significant term (represented by "li ci"; example: day) comes second, and the most significant term (represented by "li pa"; example: year) comes last, and there are exactly three terms), "li pa ce'o li ci ce'o li re" is the reverse of the last (example: YYYY-DD-MM). The point is that, while it is cumbersome, this method of filling x2 is generalizable and explicit. "Bi-endian" (traditional sense) can be specified by a judicious usage of the word ".a" between the little-endian and big-endian sequences; less conventional endiannesses which could be described as being "bi-endian" or even "n-endian" can be formed by different or more elaborate connectives between such sequences; just worry about grouping of connectives. See also: kau'ai, kau'au.