Spilt the string based on the <= 50 in one tag other wise 50 to 80 into next tag but meaning full way in xslt

Question

Example

aaaaaaaaaa bbbbbbbbbbb ccccccccccc ffffdffffdffffdffffdddheeee eeeee

1. here h is the 50th letter, 50th or 51 letter is space then copy the string next t