How to count max number of occurencies of a word in a string using XQuery

Say that i have the string "Hey how is it going hey hey" In the variable:

$Sentence

How do I receive the string "hey" since It In this example Is the word that occurs most times.

PS: I've seen examples In both Python and Javascript on this site but since I'm new to Xquery, I've had a hard time translating It.